This allows for different patterns for file names:
- lib.so.version for e.g. Linux
- lib.version.dylib for OSX (which is much more common than
lib.dylib.version)
- lib.dll for Windows (no version at all).
Refactor the SO and REV such that they are set via autoconf variables,
@so@ and @rev@. These variables are both needed by the jemalloc.sh
script, so this unifies their definitions.
