Add a super basic GimpTileBackendTileManager unit test and implement
GimpTileBackendTileManager enough to make it pass. Still a lot of work
left to do, this was just to get things up and running.

Also do some minor cleanup.

This is such a hack, but entirely safe when linking against GTK+ 2.x.
Please ignore the uglyness.

Say no to evilness.

The tinyscheme static library uses math functions, ensure that libm is
linked where necessary (#659586, original patch by Vincent Untz,
modified)

cherry-picked from commit 7df2cb45 in
the gimp-2-6 branch.

cherry-pick commit d1e0f540 from the
gimp-2-6 branch.

because it's deprecated in GLib 2.30.

Don't call gimp_input_device_store_lookup() with a NULL name. Unplug
seems broken because we always get name == NULL, I need to fix this
but at least it doesn't crash any longer (and the fix is generally
correct and not a workaround).

Introduced two virtual functions to a GimpViewable

'set_expanded' and 'get_expanded'

and a PROP_GROUP_ITEM_FLAGS to load/save the expanded state
of layer_groups and use them.

This reverts commit 359c9c22.

Add gimp_image_get_[layer|channel|vectors]_by_name().

Add an explicit search entry, so the treeview's automatic search
popup doesn't break our grab and closes the dialog in the middle
of setting up the serach popup.

From a patch by Doug Currie. Also some minor whitespace changes.

Can't call round_per_R5RS() in is_integer() as it is not available if USE_MATH
is not defined. It is simpler and faster to compare ivalue() and rvalue() of
an inexact number. No need to round integers in OP_ROUND. Minor optimization
for is_nonneg().

Based on the patch from Doug Currie.

Hide the button instead of only setting it insensitive.

Set the "eye" renderer to inconsistent state if the item is visible,
but not effectively viewable because one of its parents is invisible.

which returns TRUE if an item is effectively visible (it is visible
and all its parents are visible).

and strike out GimpCellRendererToggle's icon in the inconsistent case.

Use ngettext() instead of simply _().