autotools: Fix doc_DATA install.

Both the generated format specification document and the static
html documents depend on the logo in fish_xiph_org.png.

Unfortunately we can't list them both in their respective
dependencies because both are passed to doc_DATA for installation
and automake doesn't seem to remove duplicates, causing
/usr/bin/install to complain about the overwrite.

I couldn't find a good solution to this. Wrapping the doc_DATA
value in GNU make's $(sort /list/) function would work, but
automake warns about the non-portable construct. Instead, I've
just removed it from the spec dependency list and appended it
manually.

Author: rillian

doc/Makefile.am

@@ -29,7 +29,6 @@ static_docs = \
 # bits needed by the spec
 SPEC_PNG = \
 	components.png \
-	fish_xiph_org.png \
 	floor1-1.png \
 	floor1-2.png \
 	floor1-3.png \
@@ -98,7 +97,7 @@ DISTCLEANFILES = $(built_docs)
 
 # explicit rules for generating docs
 if BUILD_DOCS
-Vorbis_I_spec.html Vorbis_I_spec.css: $(SPEC_TEX) $(SPEC_PNG)
+Vorbis_I_spec.html Vorbis_I_spec.css: $(SPEC_TEX) $(SPEC_PNG) fish_xiph_org.png
 	htlatex $<
 
 Vorbis_I_spec.pdf: $(SPEC_TEX) $(SPEC_PNG)