%m is a glibc extension and can be replaced by %s and strerror(errno).
On systems not supporting %m, the output formerly contained a literal
%m, which will now be the real error message.
We also explititly save errno in a temporary variable saved_errno now
to make sure that e.g. the _() translation calls do not modify errno
before errno is used to determine the corresponding error message
string.
git-svn-id: https://svn.code.sf.net/p/gphoto/code/trunk/libgphoto2@12677 67ed7778-7388-44ab-90cf-0a291f65f57c
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