RFR: 1539: Allow dots in merge PR branch name [v2]

[Erik Joelsson]

> This patch makes it possible to create merge style PRs based on branches with periods `.` in the branch name. We quite commonly put periods in branch names as we like to base branches on version strings.
> 
> Modified an existing test to cover this case.

Erik Joelsson has updated the pull request incrementally with one additional commit since the last revision:

  Fix test and expand verification of valid branch names

-------------

Changes:
  - all: https://git.openjdk.org/skara/pull/1355/files
  - new: https://git.openjdk.org/skara/pull/1355/files/bb6825b9..020d07f2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1355&range=01
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1355&range=00-01

  Stats: 9 lines in 1 file changed: 0 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/skara/pull/1355.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1355/head:pull/1355

PR: https://git.openjdk.org/skara/pull/1355