ENH: change InitialPass to take a const reference to the argument string, to avoid changes to the file cache

ENH: Added find support for looking at Cable's build directory if the user sets the CABLE_BUILD_DIR cache entry.

move cygtclsh80 to the end of list, otherwise it might be found while the non-cygwin wish8x.exe will be found too. If wish8x.exe is found, then the non-cygwin tclsh8x.exe must be found too.

ENH: Added parsing of gccxml flags into separate arguments for setting the custom command.  This is necessary since the custom command now takes a vector of individual command line options instead of a single string.

Add clause to prevent adding quotes when they're already present, then stuff them
onto all lib paths to prevent forward slashes causing trouble.

with dependencies (other libraries) not linking when required. Dependency checking
required the full path to be supplied to each file when they're not in the current directory
(very tedious). All seems to be working nicely now.

add any extensions - Borland make needs full paths to certain dependencies
otherwise linking doesn't work properly (dependencies aren't checked)