autogen.sh: pass --force to autoreconf, quote string variables

By passing --force autoreconf will update all the aux files, which would
otherwise be ignored if one updates autoconf/automake.

Quote the $srcdir, $ORIGDIR and $0 variables to prevent fall-outs, when
it contains space.

v2: Also handle $srcdir and $0.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>