Simplify regeneration of build scripts by teaching gen-make.py to reuse options from a previous invocation. Currenty this only affects the Win32 build due to build generator specifics, but the feature is generic.
Simplify regeneration of build scripts by teaching gen-make.py to
reuse options from a previous invocation. Currenty this only affects
the Win32 build due to build generator specifics, but the feature is
generic.

* gen-make.py: Add new option "--reload" to re-read the gen-make.opts
  generated by the previous invocation of the script.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion