Conversion to a single libtool environment.

• devel/libtool13 is no more (requiem mors pacem)
• devel/libtool15 now installs as ${LOCALBASE}/bin/libtool etc. (ie: no versioning on the binaries and scripts)
• USE_AUTOTOOLS= libtool:XX:inc has been deprecated Where possible, ports should simply set GNU_CONFIGURE=yes and use the pre-packaged version of libtool that comes as part of the source distribution
• all the legacy hacks to libtool that we have been saddled with over the years have been removed. (eg: .la files are now installed) This brings us in line not only with Linux distributions, but also pkgsrc.
• libtool now understands, and correctly handles, "nonstandard" compilers such as g++34, gcc295, etc. etc.

This could not have happened without the truly outstanding work from kris,
not only putting up with me, but also running countless builds, both on
dosirak and pointyhat. I am truly indebted to him.

Sponsored by: Theakston Old Peculier, Marlboro Red, Cafe de Colombia
Approved by: portmgr (kris)