Improve module's abstract

Ref: http://blogs.perl.org/users/neilb/2014/07/give-your-modules-a-good-abstract.html
CheckJira: Enhance documentation for the matchlog config
GerritChangeId: Fix File::Temp::tempfile invokation

When we don't want to pass a template to tempfile we should simply not
pass it instead of passing a undef value. Weird interface...
CheckJira: Use JIRA::REST instead of JIRA::Client

The JIRA::Client module uses JIRA's SOAP API which was deprecated on
JIRA 6.0 and won't be available anymore on JIRA 7.0. So, we substitute
the JIRA::REST module which uses JIRA's newer REST API.

Note that this may break user code relying on the JIRA::Client objects
provided by the check-code configuration variable. Now the objects
provided are JIRA::REST and not JIRA::Client. Such users must rewrite
their code or create a JIRA::Client object by themselves.
Fix copyright period
Suppress 'git symbolic-ref' command errors

We redirect STDERR to /dev/null while executing the 'git symbolic-ref'
command because we don't want it to go to the user. It isn't an error
after all.
v0.048

  [Changes]
  - CheckJira now uses the JIRA::REST module instead of JIRA::Client.  The
    JIRA::Client module uses JIRA's SOAP API which was deprecated on JIRA
    6.0 and won't be available anymore on JIRA 7.0. Note that this may break
    user code relying on the JIRA::Client objects, which isn't needed for
    the hook's basic functionality.

  [Fixes]

  - Suppress spurious error message (fatal: ref HEAD is not a symbolic ref)
  when pushing a commit while in a dettached head state.
Fix JIRA::REST dependency on dist.ini

I forgot to do this before releasing version 0.048 when I substituted
JIRA::REST for JIRA::Client.

Also, the spurious Gerrit::Client dependency is removed.