move to completely self-contained prereqs using local::lib

thanks to RSRCHBOY for the suggestion
adding extlib/ as a mostly empty dir, and ignoring all contents of it
however, there is also an update-request in there which _is_ tracked
-	this insures that extlib/ will always be created when cloned
-	and it also provides a way for us to request that prereqs be updated
consolidate the code that sets up our @INC:
-	add setting up local::lib to it
-	concistencize it (as much as possible) between all the bin/ scripts
now we can make a call to Config->config_file() in bin/vctools-create-config
-	this saves some duplicated code
-	of course, now we have duplicated code to set up @INC, so I'm not sure I really got anywhere ...
bin/vctools-prereq-verify is much simpler now too:
-	we don't have to ask the user anything about how to handle `cpanm`
-	we just handle it all ourselves, since it's all local to us anyway
refactored all the "figure out all our prereqs" code into a new module
improved the generated list of prereqs in a couple of ways:
-	don't try to put Carp into the local::lib (never works)
-	don't bother putting our forever-core modules that we use to set up @INC in there either
-	make sure we add Term::ANSIColor, which didn't match our regex, manually
new safety checks:
-	make sure we have an extlib/
-	make sure we can locate `cpanm`
slight revamp of `vc self-upgrade`

now smart enough to update its prereqs, if requested by an updated extlib/update-request
better handling of errors from the `git pull`
better interleaving of output by forcing info messages to STDERR
-	(I tried setting $| to 1, but it didn't seem to help)
-	change execute() from an augment to an override
some usability tweaks for installation

change default values so you can just hit <ENTER> for everything (at Eric's request)
fix some typos
do not require a WorkingDir directive any more
can now autodiscover ~ as a WorkingDir if appropriate