FreeBSD and OpenBSD set up libs as .../libtcl83 but includes as .../include/tcl8.3 Patch allows detection on OpenBSD w/o the use of Modules/Setup.local as is currently done in the port, also allows easier Python development on that platform (build w/o using ports). This is just an enhancement of the Debian detection method. Tested on OpenBSD and Linux. Assigning to Andrew for review, he's the last to work on this section of the code. Backport 2.3 candidate?