Fix OpenAL and cURL CFLAGS for FreeBSD

changed Makefile
- Use pkg-config flags for OpenAL and cURL
Add support for loading libraries from PREFIX/lib instead of PREFIX/share

changed Makefile
changed README
- Add DEFAULT_LIBDIR

changed code/qcommon/files.c
- Add fs_libpath Cvar

changed code/qcommon/qcommon.h
- Declare Sys_SetDefaultLibPath() and Sys_DefaultLibPath()

changed code/sys/sys_main.c
- Define Sys_SetDefaultLibPath() and Sys_DefaultLibPath() and hook them up
Add DEFAULT_LIBDIR to BASE_CFLAGS for FreeBSD

changed Makefile
- Pass DEFAULT_LIBDIR on to BASE_CFLAGS in the freebsd section
Add support for custom HOMEPATH

changed Makefile
- Define default HOMEPATH .ioquake3 in the freebsd section
- Pass HOMEPATH on to BASE_CFLAGS in the freebsd section

changed README
- Add HOMEPATH to list of tunables

changed code/qcommon/q_shared.h
- Use HOMEPATH for HOMEPATH_NAME_UNIX