tcl/tk even if they are properly found by LIB_DEPENDS. Make it
only extract in that case.
While I'm here, make expect and expectk link with shared tcl/tk libs.
expectk used to be a 1/2 MB binary! (now it's 136KB)
I'd also rather change `-g' to whatever CFLAGS defined in
/etc/make.conf, but the author of expect has an explicit comment in
the Makefile about him not trusting compilers' optimization. Well,
if you say so.
