Make CommandLinePropertySource enumerable

JOpt 4.4 has enumerable options, so this change can be made
if we upgrade. The only awkward thing is that JOpt allows
aliases for options, so we have to pick one to avoid double
counting. This implementation picks the last one in the list
which is the alphebtically last of the long options, if there
are any (e.g. "o1", "option1" returns "option1"). Most of the
time there will only be one or two aliases for each option so
it won't matter.

Issue: SPR-10579
Polish pull request #291 per committer guidelines

 - Update Apache license headers
 - Remove trailing whitespace
 - Edit original commit comment to use 'Issue:' syntax
 - Revert use of diamond operator (<>) in main sources

See committer guidelines at
https://github.com/SpringSource/spring-framework/blob/master/CONTRIBUTING.md

Issue: SPR-10579
Merge pull request #291 from dsyer/10579

# By Chris Beams (1) and Dave Syer (1)
* SPR-10579:
  Polish pull request #291 per committer guidelines
  Make CommandLinePropertySource enumerable