Remove virtual readPixel() function from RenderDevice

This function is only used by SDLSoftwareRenderDevice, so it doesn't
need to be declared for all render devices.
Remove dstrect parameter from fillWithColor()

All of our uses for this function were passing NULL to this variable in
order to fill the entire image surface.
Fix potential invalid iterator bug
Merge pull request #1225 from dorkster/coverity

Fix potential invalid iterator bug
Always show quantity in tooltips when quantity > 1

Sometimes, it's difficult to read the quantity that's displayed on the
icon, especially for quantities > 100. This provides some easier to read
text in the item tooltip.
Merge pull request #1224 from dorkster/renderer

Remove virtual readPixel() function from RenderDevice
Merge pull request #1226 from dorkster/item_tooltips

Always show quantity in tooltips when quantity > 1
Add SDL hardware renderer

This renderer uses the GPU-based SDL_Texture the is part of SDL 2. To
use the renderer, launch Flare with:

    flare --renderer=sdl_hardware

Known issues:
- Text looks "narrower" than with the SDL software renderer. This is
because the software renderer uses `SDL_gfxBlitRGBA()`, which uses
a non-linear alpha table to make things appear brighter.
Merge pull request #1229 from dorkster/next

Add SDL hardware renderer
Fix bugs in HW renderer found by Coverity scan
Merge pull request #1230 from dorkster/coverity

Fix bugs in HW renderer found by Coverity scan
Compare colors when comparing TooltipData

Closes #1231
Merge pull request #1233 from dorkster/tooltip_compare

Compare colors when comparing TooltipData
Remove blank function
Don't try to swap stash stacks when dropping from inventory

Possibly related to #1232. This ensures that if we drop an inventory
item on a non-empty stash slot, it will be added to an empty slot and
not treated as if we're rearranging stash contents.
Allow equipping items dragged in from stash/vendor
Merge pull request #1234 from dorkster/menus

Drag & drop tweaks
Update actionbar after upgrading powers