Make caller-allocates detection work for struct aliases

Make caller-allocates detection work for struct aliases

Scanner tries to detect caller-allocates attribute automatically if
not explicitly specified by checking that parameter is not double-referenced
and is struct or union.  This patch adds resolving of aliases when
checking whether parameter is struct or union.

Also removes old incorrect method transformer.follow_aliases, which
was never used in current code.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=639081