For each pixel format we store a flag in the table whether it supports
post pixelshader blending. Before applying blending or during a
context switch we verify that blending is turned off for the
format. In case of R32F this gave a 5-6x performance boost (without
filtering and software conversion).

widl: Make sure that string types are always written out by write_string_tfs and not write_simple_pointer.

This is because write_string_tfs has support for the full range of 
string types, write_simple_pointer doesn't have access to the var 
attributes which are needed to properly detect strings, and 
write_string_tfs sets the typestring offset to after the pointer is 
written and write_remoting_arg depends on this.

is_ptr cannot be used because it follows the chain of types into the 
type which has the context_handle attribute, which is typically "void *" 
and so causes these context handles to be incorrectly detected as 
context handles. Instead, we can use is_aliaschain_ptr to follow the 
chain of aliases without following pointers and the absence of the 
context_handle attribute indicates that it must be present on a type 
after following a pointer.