EXECVERSION adjustments (config updater)

Made the following changes to the EXECVERSION scheme:

• Split cv_execversion from MODVERSION -- use separate EXECVERSION define instead, comprised of MAJOREXECVERSION and MINOREXECVERSION digits stored in the same value.
  • Minor version is left-shifted 16 bits. Macros written to facilitate this scheme.

MAJOREXECVERSION is intended to be equal to MODVERSION, due to my previous decision to tie this feature to MODVERSION. That may have been foolish, but I think keeping track of another set of version numbers would get messy.

I would have liked to use VERSION and SUBVERSION instead, but those are zero'd out in DEVELOP builds.

MINOREXECVERSION is intended for any time when a config update is required, but MAJOREXECVERSION is not incremented. In practice, this might never be used.