[bug-gettext] Gettext incorreclty detects C format

[Urmas]

The strings which have literal '%' sign in the string (like "% done") are 
flagged as c-format, which they obviously aren't. Please fix detection in that 
particular case, as the probability that such combination is a format string, 
is extremely low, and no counter-intuitive no-c-format flag should have to be 
used in that case.