issue 2533 continued: fix problematic uses of line-count in bar-line (issue 6441166)

[benko . pal]

Reviewers: marc, Keith, dak,

Message:
all changes in a single commit; I'm happy to resubmit it in four; I can
also push (after review and coutdown) in one or four or as you wish.

Description:
issue 2533 continued: fix problematic uses of line-count in bar-line

- modify regtests to show when to put the dots of a repeat sign
  inside or outside the staff
- make same dots
  - be centred on the staff centre,
  - avoid staff lines,
  - be far enough when there are no staff lines
- extend or shrink bar line if it's too short or long

Please review this at http://codereview.appspot.com/6441166/

Affected files:
  M input/regression/repeat-sign-global-size-10.ly
  M input/regression/repeat-sign-global-size-30.ly
  M input/regression/repeat-sign-layout-size.ly
  M scm/bar-line.scm