Add the possibility to pass --flag arguments to xgettext calls

The --flag argument can be used to tell xgettext the arguments of
which functions should be flagged with c-format in the PO files,
instead of guessing based on the presence of format specifiers, which
fails if no format specifiers are present but the translation
accidentally introduces one.

Appropriate flag settings have been added for each message catalog.

based on a patch by Christoph Berg for bug #6066

src/pl/plperl/nls.mk

@@ -3,3 +3,4 @@ CATALOG_NAME     = plperl
 AVAIL_LANGUAGES  = de es fr it ja pt_BR ro tr zh_CN zh_TW
 GETTEXT_FILES    = plperl.c SPI.c
 GETTEXT_TRIGGERS = $(BACKEND_COMMON_GETTEXT_TRIGGERS)
+GETTEXT_FLAGS    = $(BACKEND_COMMON_GETTEXT_FLAGS)

src/pl/plpgsql/src/nls.mk

@@ -3,3 +3,4 @@ CATALOG_NAME     = plpgsql
 AVAIL_LANGUAGES  = de es fr it ja ko pt_BR ro zh_CN zh_TW
 GETTEXT_FILES    = pl_comp.c pl_exec.c pl_gram.c pl_funcs.c pl_handler.c pl_scanner.c
 GETTEXT_TRIGGERS = $(BACKEND_COMMON_GETTEXT_TRIGGERS) yyerror plpgsql_yyerror
+GETTEXT_FLAGS    = $(BACKEND_COMMON_GETTEXT_FLAGS)

src/pl/plpython/nls.mk

@@ -3,3 +3,8 @@ CATALOG_NAME     = plpython
 AVAIL_LANGUAGES  = de es fr it ja pt_BR ro tr zh_CN zh_TW
 GETTEXT_FILES    = plpython.c
 GETTEXT_TRIGGERS = $(BACKEND_COMMON_GETTEXT_TRIGGERS) PLy_elog:2 PLy_exception_set:2 PLy_exception_set_plural:2,3
+GETTEXT_FLAGS    = $(BACKEND_COMMON_GETTEXT_FLAGS) \
+    PLy_elog:2:c-format \
+    PLy_exception_set:2:c-format \
+    PLy_exception_set_plural:2:c-format \
+    PLy_exception_set_plural:3:c-format

src/pl/tcl/nls.mk

@@ -3,3 +3,4 @@ CATALOG_NAME     = pltcl
 AVAIL_LANGUAGES  = de es fr it ja pt_BR ro tr zh_CN zh_TW
 GETTEXT_FILES    = pltcl.c
 GETTEXT_TRIGGERS = $(BACKEND_COMMON_GETTEXT_TRIGGERS)
+GETTEXT_FLAGS    = $(BACKEND_COMMON_GETTEXT_FLAGS)