Many of the messages in gthumb have whitespace before colons, points,
question marks and excalamation marks, like these examples:

#: libgthumb/catalog-png-exporter.c:1294
#, c-format
msgid "Loading image : %s"

#: src/commands-impl.c:470
msgid "The image will be moved to the Trash, are you sure ?"

While this practice with whitespace before colons and question marks may be
correct in French and possibly also Italian, I doubt it is correct English.
Moreover, it's inconsistent with most other GNOME software, and
inconsistencies like this cause problems for, among others, translators
that want to re-use already translated messages.

I thus suggest that all whitespaces before colons and the other marks
mentioned above be removed from all gthumb messages.