* docs/html/ext/howto.html: Update commentary.
* include/bits/c++config: Update threading configuration comment.
(__STL_GTHREADS): Remove macro definition.
(__STL_THREADS): Likewise.
* include/bits/stl_threads.h: Leave only the configuration
path which had been guarded by __STL_GTHREADS. Remove all
guards related to __STL_GTHREADS, __STL_SGI_THREADS,
__STL_PTHREADS, __STL_UITHREADS and __STL_WIN32THREADS.
* include/bits/stl_alloc.h: Leave only the configuration path
which had been guarded by __STL_THREADS. Remove configuration
path and guards for __STL_SGI_THREADS.
(__NODE_ALLOCATOR_THREADS): Remove macro definition. Unroll its use.
(__NODE_ALLOCATOR_LOCK): Likewise.
(__NODE_ALLOCATOR_UNLOCK): Likewise.
(_NOTHREADS): Remove guards related to macro.
* include/ext/stl_rope.h: Remove configuration path and guards
for __STL_SGI_THREADS.
* src/stl-inst.cc: Remove use of __NODE_ALLOCATOR_THREADS.
From-SVN: r47557
