add support for 'ccache' program to cmake script
add support for 'ccache' program to cmake script

if ccache is available on the user's system, then we assume that
they are a developer and that they want to use it.

If people want, we could add an option to disable the use of
ccache even if it is present.

--HG--
branch : ccache

cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two