#1453 (GTK) tab markers not visible if indent markers are visible

[Mark Yen]

On GTK only (couldn't reproduce with Win32 or OSX), when you have both tab markers and indent markers turned on, only the first tab marker (before any indents) are visible. This can be seen in a document like: (where "#" is a tab)

a

See attached patch - the issue seems to be that, in line drawing, the order is
- set pen colour
- draw indents
- draw tabs
But, on GTK/cairo, drawing indents involves setting the source surface (to copy from), which reset the pen colour. The patch changes it to
- draw indents
- set pen colour
- draw tabs
Which doesn't have this problem.

[Neil Hodgson]

While the patch makes sense, I was unable to reproduce the problem on GTK+ 2 or 3 on Mint Linux 14.
A simplified version committed as [09444c].