Reorganize include files to avoid conflicts with other libs
- Change all header includes to be relative to the project root
- Remove -I${includedir} from bitlbee.pc Cflags
- Install lib and protocols headers to their own directories. So now it is:
/usr/include/bitlbee/*.h
/usr/include/bitlbee/lib/*.h
/usr/include/bitlbee/protocols/*.h
This breaks backwards compatibility of third party plugins, but now
they don't have to do ambiguous includes like #include <proxy.h>
This also fixes trac ticket 1170 - conflicts when libproxy and liboauth
are installed at the same time bitlbee is built, which the macports
project ran into several times.
