Improve support for SOURCE_DATE_EPOCH by forcing UTC timezone

The patch in PR #69 and its extension in commit 39936be did not address
the reproducibility issues that arise when different timezones are used.

The Reproducible Builds project suggests forcing the use of the UTC timezone
whenever `SOURCE_DATE_EPOCH` is used.

Author: gioele

main/java/BitsNPicas/src/com/kreative/bitsnpicas/Font.java

@@ -450,6 +450,7 @@ public void autoFillNames() {
 			if (sourceDateEpochEnv != null) {
 				long sourceDateEpoch = Long.parseLong(sourceDateEpochEnv);
 				now.setTimeInMillis(sourceDateEpoch * 1000L);
+				now.setTimeZone(TimeZone.getTimeZone("UTC"));
 			}
 			names.put(NAME_UNIQUE_ID, "BitsNPicas: " + pname + ": " + now.get(Calendar.YEAR));
 		}

main/java/BitsNPicas/src/com/kreative/bitsnpicas/edit/TimestampGlyphGenerator.java

@@ -2,6 +2,7 @@
 
 import java.util.GregorianCalendar;
 import java.util.List;
+import java.util.TimeZone;
 import com.kreative.bitsnpicas.BitmapFontGlyph;
 import com.kreative.bitsnpicas.Font;
 
@@ -17,6 +18,7 @@ public Result generate(Font<BitmapFontGlyph> font, List<GlyphLocator<BitmapFontG
 		if (sourceDateEpochEnv != null) {
 			long sourceDateEpoch = Long.parseLong(sourceDateEpochEnv);
 			now.setTimeInMillis(sourceDateEpoch * 1000L);
+			now.setTimeZone(TimeZone.getTimeZone("UTC"));
 		}
 
 		BitmapFontGlyph[] glyphs = getTimestampGlyphs(font, now);

main/java/BitsNPicas/src/com/kreative/bitsnpicas/exporter/OTBBitmapFontExporter.java

@@ -12,6 +12,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.TimeZone;
 import com.kreative.bitsnpicas.BitmapFont;
 import com.kreative.bitsnpicas.BitmapFontExporter;
 import com.kreative.bitsnpicas.BitmapFontGlyph;
@@ -256,6 +257,7 @@ private static final HeadTable makeHeadTable(BitmapFont bf, ThingsToKeepTrackOf
 		if (sourceDateEpochEnv != null) {
 			long sourceDateEpoch = Long.parseLong(sourceDateEpochEnv);
 			now.setTimeInMillis(sourceDateEpoch * 1000L);
+			now.setTimeZone(TimeZone.getTimeZone("UTC"));
 		}
 
 		double fontVersion;

main/java/BitsNPicas/src/com/kreative/bitsnpicas/exporter/TTFBitmapFontExporter.java

@@ -10,6 +10,7 @@
 import java.util.GregorianCalendar;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.TimeZone;
 import com.kreative.bitsnpicas.BitmapFont;
 import com.kreative.bitsnpicas.BitmapFontExporter;
 import com.kreative.bitsnpicas.BitmapFontGlyph;
@@ -234,6 +235,7 @@ private static final HeadTable makeHeadTable(BitmapFont bf, ThingsToKeepTrackOf
 		if (sourceDateEpochEnv != null) {
 			long sourceDateEpoch = Long.parseLong(sourceDateEpochEnv);
 			now.setTimeInMillis(sourceDateEpoch * 1000L);
+			now.setTimeZone(TimeZone.getTimeZone("UTC"));
 		}
 
 		double fontVersion;

main/java/BitsNPicas/src/com/kreative/bitsnpicas/geos/CBMDirectoryBlock.java

@@ -6,6 +6,7 @@
 import java.io.UnsupportedEncodingException;
 import java.util.Calendar;
 import java.util.GregorianCalendar;
+import java.util.TimeZone;
 
 public class CBMDirectoryBlock implements CBMConstants {
 	public static final String COMMENT_PRG = "PRG formatted GEOS file";
@@ -53,6 +54,7 @@ public void clear() {
 		if (sourceDateEpochEnv != null) {
 			long sourceDateEpoch = Long.parseLong(sourceDateEpochEnv);
 			now.setTimeInMillis(sourceDateEpoch * 1000L);
+			now.setTimeZone(TimeZone.getTimeZone("UTC"));
 		}
 
 		year = now.get(Calendar.YEAR);

main/java/BitsNPicas/src/com/kreative/bitsnpicas/main/ConvertBitmap.java

@@ -11,6 +11,7 @@
 import java.util.Map;
 import java.util.Scanner;
 import java.util.Set;
+import java.util.TimeZone;
 import java.util.regex.Pattern;
 import java.util.regex.PatternSyntaxException;
 import com.kreative.bitsnpicas.BitmapFont;
@@ -582,6 +583,7 @@ private static void transformFont(BitmapFont font, Options o) {
 			if (sourceDateEpochEnv != null) {
 				long sourceDateEpoch = Long.parseLong(sourceDateEpochEnv);
 				now.setTimeInMillis(sourceDateEpoch * 1000L);
+				now.setTimeZone(TimeZone.getTimeZone("UTC"));
 			}
 
 			BitmapFontGlyph[] glyphs = TimestampGlyphGenerator.getTimestampGlyphs(font, now);