Split the mysql/client rules by major.minor version

As of MySQL 5.5 and later, the code uses cmake to build, instead of
GNU configure.  This is very unfortunate, because cmake (which has
UGLY ALL CAPS SYNTAX!!), or at least the cmake configurations as
written for MySQL, do not allow the easy specification of alternate
locations for dependencies, making it very difficult to build the
product against EFS-based things like openssl.

For now, we're just going to use MySQL 5.1, and revisit the cmake
integration at a future date.  The database used by EFS itself may
change in the near future anyway.
python/core needs the widec versions of ncurses

Python is the first dependency I've come across that needs to use the
widec versions of the ncurses libraries.
Make the expansion of the perl5/core dependency a hard requirement

I can't seem to reproduce it, but during a couple of builds, we've
ended up with the value of the perl5/core dependency being an empty
string, so die if that happens again.