Makefile.autotools.in: Extended to cope with more bad packages

1. I added a HOOK_POST_EXTRACT previously so that I could cope with the
bad libxml2 package.  This required me to remove some dead patches
(.rej) files after I extracted the package, the issue is that the
EXTRACT target runs patch-kernel.sh to patch the ltmain.sh.  
It then finds some.rej files and bombs out.
I have altered the sequence so that the HOOK_POST_EXTRACT target runs
before the make target that patches libtool to deal with this.
 
2.) I have added a $(PKG)_LIBTOOL_PATCH variable.  This is defaulted to
YES however if you override it in the package makefile to NO then the
ltmain.sh file will not be patched automatically but only if you have
added your own patches.  
This is necessary for freetype 2.3.7 as it cannot use the
buildroot-libtool patch.

I am using this patch for building a set of packages, however it
is not a complete set of packages so await feedback of issues (if any)

Daniel Laird