Respect apiversion in overrides

We should not use overrides from foreign apiversions.
Strongly-typed enums for ES 3.0 (WIP3)

Implemented sections: Texturing, Sampler Objects, Sampler Queries,
Texture Image Specification.
Added "reuse" directive for enums

Sometimes an enum may reuse the tokens of another enum verbatim
(possibly adding a few extra tokens.) The reuse directive simplifies
the handling of this case:
<enum name="Foo">
  <reuse enum="Bar" />
</enum>
Strongly-typed enums for ES 3.0 (WIP4)

Implemented sections: Texture Image Specification, Alternative Texture
Image Specification, Compressed Texture Images, Texture Parameters,
Manual Mipmap Generation and Enumerated Queries.
Strongly-typed enums for ES 3.0 (WIP5)

Implemented sections: Stencil Test, Depth Buffer Test, Blending.
Strongly-typed enums for ES 3.0 (WIP6)

Implemented strongly-typed enums for sections: Selecting a Buffer for
Writing, Fine Control of Buffer Updates, Clearing the Buffers.
Implemented support for <overload> element

The <overload> element simplifies the addition of overloads for
backwards compatibility. It is defined similar to the <replace>
element, but instead of replacing the parameters of a function
in-place, it adds a new overload and modifies the overload instead.
Moved overload to overrides.xml

Overloads for backwards compatibility should now be placed in an
<overload> element inside overrides.xml.
Strongly-typed enums for ES 3.0 (WIP7)

Implemented section: Sync Objects and Fences [5.2].
Fixed desktop OpenGL wrapper for ClientWaitSync and FenceSync.
Strongly-typed enums for ES 3.0 (WIP8)

Implemented sections: Hints and Sync Object Quries.
Renamed SyncParameter to SyncParameterName, as per the OpenGL naming
conventions.
Added workaround for issue #6

The issue is that some display devices report a BitsPerPel value of 0.
It is not clear whether this is a bug in WinDisplayDevice.cs or some
strange windows issue. The implemented workaround adds an entry to the
debug log and hardcodes BitsPerPel to 32 whenever this condition is
encountered. More investigation required.
Switch to EnumDisplayModesEx

Use EnumDisplayModesEx instead of EnumDisplayModes. This might help
with issue #6.
Fixed number of buffers

ContextAttribute.DOUBLEBUFFER is a boolean in SDL (false->single
buffering, true->double buffering). We need to adjust the number of
buffers accordingly (single buffering->1 buffer, double buffering->2
buffers).
Strongly-typed enums for ES 3.0 (complete)

Implemented sectiosn: Pixel Rectangles. Binding & Managing Framebuffer
Objects, Renderbuffer Objects, Attaching Renderbuffer Images to
Framebuffer, Attaching Texture Images to Framebuffer, Framebuffer
Completeness, Invaildating Framebuffer Contents, Renderbuffer Object
Queries, Simple Queries, String Queries.
Merge branch 'master' of https://github.com/thefiddler/opentk
Fixes for ES 3.0 strongly-typed enums

Fixed parameter mismatches in CopyBufferSubData and BlendFuncSeparate.
Implemented KHR_debug extension.
Fixed strong-enums for GetDebugMessageLog

GetDebugMessageLog is part of KHR_debug.
Fixed enums for GetDebugMessageLog

GetDebugMessageLog was misspelled as GetMessageDebugLog. This is now
fixed.
Fixed enums for (Get)ObjectLabel

ObjectLabel and GetObjectLabel are part of KHR_debug.
Fixed misspelled and missing enums