MacOSX mysql install location

[Alex Burton]

Hi Warren,

./configure needed to have --with-mysql=/usr/local/mysql argument,  
when building mysql++2.3.2
after installing latest mysql .dmg

I couldn't figure out what to do with those m4 files to change the  
paths in there, but figured out --with in the end. Might be nice to  
add this path so that ./configure works out of the box.

Alex