Merge pull request #1 from sergiomb2/master

missed libdir = @RAWSTUDIO_PLUGINS_LIBS_DIR@
Merge pull request #2 from sergiomb2/master

insert missed DESTDIR. Fixes Fedora package build.
No need to check if an unsigned is below zero :)
Fixed a few compiler warnings.
Fixed compiler warning.
also remove librawstudio.la and librawstudio.a (if exist)
Merge github.com:rawstudio/rawstudio