The --version-sort option requires strverscmp(), but this is a glibc
extension that does not exist on OpenBSD and other systems. To enable
--version-sort on those systems, provide an internal implementation of
strverscmp(). The implementation is from the musl C library and is
MIT-licensed.

The build process remains the same: the verscmp flag should be set to 1
only if strverscmp() is available in libc. If verscmp is 0, then the
internal implementation is used.

might resolve #333 and #348

(see #337)

This reverts commit 465238bd.

This should also help distributions working towards reproducible builds.

They have been deprecated since 2011 and may be removed entirely in future
versions.

- fixed uninitialized pointer in thumbnail mode
- added nikon lens info if available

- fixed uninitialzed pointer in thumbnail mode
- added nikon lens info if available