windows: Show the open dialog on a separate thread.

Allows the screen to continue rendering, which should prevent black
screens, etc. while browsing.

May help #2755.
Allow texture scaling on changed textures.

But only if they don't change very frequently.  Should fix #1934.
Disable scaling to odd multiples when unsupported.

May help #4000.
Don't bother writing an empty symbol map.

For example, when accidentally opening an invalid file.
softgpu: Don't redraw every pixel of a line 16x.

Fixes the insane slowness when processing lines.  Now it's just regular
super slow.
softgpu: Avoid a divide by 0 in line interpolation.

Fixes crash in Persona 2 loading screens.
softgpu: Fix lines drawn upward or leftward.
Merge pull request #5152 from unknownbrackets/ui-tweaks

Show the Windows open dialog on a separate thread
Merge pull request #5155 from unknownbrackets/texscaling

Disable scaling to odd multiples when unsupported.
Merge pull request #5153 from unknownbrackets/texcache2

Allow texture scaling on changed textures
Merge pull request #5158 from unknownbrackets/softgpu

Fix a bunch of issues in line drawing in softgpu
windows: Re-enable scaling on gl_extensions change.

This fixes the fact that it's not filled in the first time UpdateMenus()
is called, since it's called again whenever you open the menu anyway.
windows: Ignore key/mouse input while menu focused.

This prevents arrow and shortcut keys from being considered inputs to the
game or UI.
Don't call SetTexture() in clear mode.

It's just a waste of time, the game is probably being lazy.
Change the self message for separate reporting.
Merge pull request #5161 from unknownbrackets/texcache2

Don't call SetTexture() in clear mode
Merge pull request #5160 from unknownbrackets/ui-tweaks

windows: Ignore key/mouse input while menu focused
Report block transfers we don't support.

Ones involving framebuffers.
Merge pull request #5162 from unknownbrackets/reporting

Report block transfers we don't support
Put depth copy as BindFramebufferDepth()