Fails to compile (link) because of missing -lm in LIBADD (in Makefile.am). Will attach a patch.

This was reported by Jeremy Olexa from Gentoo

/home/jolexa/portage/linux-64/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.3/../../../../x86_64-pc-linux-gnu/bin/ld: lib/.libs/libscreenshooter.a(lib_libscreenshooter_la-katze-throbber.o): undefined reference to symbol 'floorf@@GLIBC_2.2.5'
/home/jolexa/portage/linux-64/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.3/../../../../x86_64-pc-linux-gnu/bin/ld: note: 'floorf@@GLIBC_2.2.5' is defined in DSO /lib64/libm.so.6 so try adding it to the linker command line
/lib64/libm.so.6: could not read symbols: Invalid operation
collect2: ld returned 1 exit status
make[2]: *** [src/xfce4-screenshooter] Error 1