Bypass autoscan's recommendation of AC_FUNC_MALLOC or AC_FUNC_REALLOC

This should fix https://github.com/fontforge/fontforge/issues/384 in terms
of AC_FUNC_MALLOC and AC_FUNC_REALLOC so if someone runs autoscan it won't
get re-inserted to test for this again.
Merge pull request #387 from JoesCat/2013mar5_AC_FUNC_REALLOC

Bypass autoscan's recommendation of AC_FUNC_MALLOC or AC_FUNC_REALLOC