Next wave:
o Change mjpegtools version to 1.7.0 --- seriously, so much has changed!
o Reinstated --with-jpeg-mmx.
o Added --without-png option.
o Put AM_CONDITIONAL's closer to where the actual decisions are made.
o Replaced all the pthread stuff with ACX_PTHREAD.
o Use AC_PATH_LIB() for libquicktime.
o Tidied the X finding stuff.
o Created "acinclude.m4" with extra macros.
