COMP: Review use of iostream & use double-conversion where needed
Merge pull request #187 from Chaircrusher/IOStreamDoubleConversion

COMP: Review use of iostream & use double-conversion where needed
COMP: Avoid continuous rebuild of ExternalPackages

New option added to that defaults to off for FORCE_EXTERNAL_BUILDS.
This needs to be turned ON to allow updating of external packages.

Needed to split the ExternalProject command and argument into separate
varables for their effect to work.  Otherwise they were having no
noticiable effect on the build system.