Structure: use TextIters instead of line numbers

It simplifies the code, and it's slightly faster.
Revert "Structure: remove hack due to old Vala bug"

This reverts commit a9527968f33aa1026c6859680fe593185f772a06.

It seems that the bug is actually not fixed.
Comment about a hack due to a bug in vala

The bug #652781 is fixed, but here it's another similar bug.

http://gnomememes.tumblr.com/post/23749155851/its-a-trap
CMake: option to change the man page directory

This will avoid a patch in the OpenBSD port.
CMake: find glib-compile-resources executable
Icon size available in 192x192

It would have been better to have a 256x256 size, and also a scalable
(SVG) one, but the original icon is in PNG with a size of 165x195. So
192x192 is the nearest (and other applications ship a 192x192 icon size
as well).

Fixes bug #679174:
https://bugzilla.gnome.org/show_bug.cgi?id=679174
Remove useless comments
Symbols: fix a fixme
Remove commented code
Build Tools: new UI for the preferences

Move the UI from the .ui file to a new .vala. Use a more modern,
GNOME 3-friendly toolbar for the buttons, with symbolic icons.
Build Tools preferences: buttons's sensitivity
Build Tools: remove the 'must succeed' option

It's better to always abort when a command fails. I think nobody has
ever used this option…
Build Tools: adapt the documentation

Since the 'must succeed' option has been removed.
Updated POTFILES.in
Build Tools: left margin in the preferences
Build tool dialog: beginning of the cleanup
Build tool dialog: mini-toolbar buttons (UI)
Build tool dialog: behavior and sensitivity of the toolbar buttons
Build tool dialog: edit and create a build tool
Build tool dialog: the final bits