Locate AVIFILE library and include paths

AVIFILE ( a set of libraries for i386 machines to use various AVI codecs. Support is limited beyond Linux. Windows provides native AVI support, and so doesn’t need this library. This module defines

AVIFILE_INCLUDE_DIR, where to find avifile.h , etc.
AVIFILE_LIBRARIES, the libraries to link against
AVIFILE_DEFINITIONS, definitions to use when compiling
AVIFILE_FOUND, If false, don't try to use AVIFILE