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Make COMMON_LIBRARY_TYPE a cache property

Using static or shared libraries really is a system decision (cf. BGQ
performance with DSOs) -- Consequently one wants to setup the whole
build shared or static. This change makes this a cache property, and a
follow-on Buildyard change will propagate the setting from BY to all
projects. An even later change will probably auto-detect the target
platform and set COMMON_LIBRARY_TYPE accordingly.
Fix package config failure handling (partial #240)
macro to find a dependency consistently (#240)
Use CommonPackage in PackageConfig (#240)
Add default license
Documentation for CommonPackage
CommonPackage: Implement quiet and fix parsing (#240)
GitExternals: fix checkout-on-update
CommonPackage: fix version with empty args
Merge branch 'master' into superproject