Include header files in pot-updates

It would probably be better to avoid using translatable strings in headers,
but certain people keep doing so anyway, so this is more future-proof.

cmake/update_pot_source_dependencies.cmake

@@ -25,7 +25,7 @@ if(DOMAIN STREQUAL ${DEFAULT_DOMAIN})
 				-E touch ${PROJECT_SOURCE_DIR}/po/${DOMAIN}/POTFILES.in
 
 		# Find all cpp files which are not in a .git directory.
-		COMMAND find src  -name .git -prune -o -name '*cpp' -print |
+		COMMAND find src  -name .git -prune -o -name '*.[hc]pp' -print |
 				sort |
 				while read file\; do
 					# If the file doesn't contain a GETTEXT_DOMAIN

po/SConscript

@@ -32,7 +32,7 @@ if "pot-update" in COMMAND_LINE_TARGETS:
     domain_sources = defaultdict(list)
     def fill_source_list(arg, dir, files):
         for file in files:
-            if fnmatch(file, "*.cpp"):
+            if fnmatch(file, "*.[hc]pp"):
                 match = re.search('^#define\\s+GETTEXT_DOMAIN\\s+"wesnoth(-.*)"', Dir(dir).File(file).get_contents(), re.MULTILINE)
                 if match:
                     source_domain = match.group(1)