config: use config_error_nonbool() instead of custom messages

A few config callbacks use their own custom messages to report an
unexpected implicit bool like:

  [merge "foo"]
  driver

These should just use config_error_nonbool(), so the user sees
consistent messages.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

imap-send.c

@@ -1346,7 +1346,7 @@ static int git_imap_config(const char *var, const char *val,
 		server.port = git_config_int(var, val, ctx->kvi);
 	else if (!strcmp("imap.host", var)) {
 		if (!val) {
-			return error("Missing value for 'imap.host'");
+			return config_error_nonbool(var);
 		} else {
 			if (starts_with(val, "imap:"))
 				val += 5;

merge-ll.c

@@ -301,7 +301,7 @@ static int read_merge_config(const char *var, const char *value,
 
 	if (!strcmp("driver", key)) {
 		if (!value)
-			return error("%s: lacks value", var);
+			return config_error_nonbool(var);
 		/*
 		 * merge.<name>.driver specifies the command line:
 		 *

xdiff-interface.c

@@ -314,7 +314,7 @@ int git_xmerge_config(const char *var, const char *value,
 {
 	if (!strcmp(var, "merge.conflictstyle")) {
 		if (!value)
-			return error(_("'%s' is not a boolean"), var);
+			return config_error_nonbool(var);
 		if (!strcmp(value, "diff3"))
 			git_xmerge_style = XDL_MERGE_DIFF3;
 		else if (!strcmp(value, "zdiff3"))