#115 Adapt FindGLIB2.cmake to work with vcpkg

[letmaik]

I'd like to use the vcpkg package manager for Windows for lensfun's glib2 dependency (and its dependencies).

There is a minor patch to be made to cmake/modules/FindGLIB2.cmake to make it work. This is because in vcpkg, the final package structure is such that glibconfig.h resides in ${GLIB2_BASE_DIR}/include. Can you add this search path to the FIND_PATH(GLIB2_GLIB2CONFIG_INCLUDE_PATH call?

[seebk]

Sure, have fixed it in master.