Implement in-place release with -i/--inplace option

[baby-gnu]

This implement a solution to issue #133 "Add ability to release directly
from develop".

When in-place is activated:

• the current branch must be merged in the develop branch
• no mergeback occurs
• no branch deletion occurs

The in-place release can be called in two ways:

git flow release finish -i <version>

or a shorter form:

git flow release -i <version>

• git-flow-release (cmd_default): Define flags of cmd_list() and
  cmd_finish() to support the shorter call form.
  Call cmd_finish() if inplace is enabled.
  (cmd_list): Avoid warning by redefining the verbose flag if called from
  cmd_default().
  (cmd_finish): Avoid warning by redefining flags if called from
  cmd_default().
  Add filter on the version.
  Do not merge back and delete branch when inplace is enabled

[petervanderdoes]

I won't implement the shorter version git flow release -i <version> as this messes up when you run git flow release -h and the flags shown do not apply to git flow release

$ git flow release -h
USAGE: git flow release [flags] args
flags:
  -h,--[no]help:  show this help (default: false)
  -F,--[no]fetch:  fetch from origin before performing finish (default: false)
  -s,--[no]sign:  sign the release tag cryptographically (default: false)
  -u,--signingkey:  use the given GPG-key for the digital signature (implies -s) (default: '')
  -m,--message:  use the given tag message (default: '')
  -p,--[no]push:  push to origin after performing finish (default: false)
  -k,--[no]keep:  keep branch after performing finish (default: false)
  -n,--[no]notag:  don't tag this release (default: false)
  -b,--[no]nobackmerge:  don't back-merge master, or tag if applicable, in develop  (default: false)
  -i,--[no]inplace:  Release directly on the development branch (default: false)
  -v,--[no]verbose:  verbose (more) output (default: false)
USAGE: git flow release [flags] args
flags:
  -h,--[no]help:  show this help (default: false)
  -F,--[no]fetch:  fetch from origin before performing finish (default: false)
  -s,--[no]sign:  sign the release tag cryptographically (default: false)
  -u,--signingkey:  use the given GPG-key for the digital signature (implies -s) (default: '')
  -m,--message:  use the given tag message (default: '')
  -p,--[no]push:  push to origin after performing finish (default: false)
  -k,--[no]keep:  keep branch after performing finish (default: false)
  -n,--[no]notag:  don't tag this release (default: false)
  -b,--[no]nobackmerge:  don't back-merge master, or tag if applicable, in develop  (default: false)
  -i,--[no]inplace:  Release directly on the development branch (default: false)
  -v,--[no]verbose:  verbose (more) output (default: false)

Instead of:

$ git flow release -h
USAGE: git flow release [flags] args
flags:
  -h,--[no]help:  show this help (default: false)
  -v,--[no]verbose:  verbose (more) output (default: false)

[baby-gnu]

I'm fine with this, I should have done two commit as I was not sure for the shorter form.

The shorter form would be possible if shFlags permit to ignore unknown flags, say cmd_default() define only -h, -v and -i and tells shFlags to ignore all the others.
But shFlags code is quite difficult to enter into ;-)