Issue #18149: Add filecmp.clear_cache() to manually clear the filecmp cache.
Patch by Mark Levitt
Issue #17222: Raise FileExistsError when py_compile.compile would
overwrite a symlink or non-regular file with a regular file.
merge
Issue #3329: Add new APIs to customize memory allocators

* Add a new PyMemAllocators structure
* New functions:

  - PyMem_RawMalloc(), PyMem_RawRealloc(), PyMem_RawFree(): GIL-free memory
    allocator functions
  - PyMem_GetRawAllocators(), PyMem_SetRawAllocators()
  - PyMem_GetAllocators(), PyMem_SetAllocators()
  - PyMem_SetupDebugHooks()
  - _PyObject_GetArenaAllocators(), _PyObject_SetArenaAllocators()

* Add unit test for PyMem_Malloc(0) and PyObject_Malloc(0)
* Add unit test for new get/set allocators functions
* PyObject_Malloc() now falls back on PyMem_Malloc() instead of malloc() if
  size is bigger than SMALL_REQUEST_THRESHOLD, and PyObject_Realloc() falls
  back on PyMem_Realloc() instead of realloc()
* PyMem_Malloc() and PyMem_Realloc() now always call malloc() and realloc(),
  instead of calling PyObject_Malloc() and PyObject_Realloc() in debug mode
Issue #18192: Introduce importlib.util.MAGIC_NUMBER and document the
deprecation of imp.get_magic().
Issue #17907: Document types.ModuleType's constructor and attributes,
allowing for documenting imp.new_module() as deprecated.
Closes issue 17947.  Adds PEP-0435 (Adding an Enum type to the Python standard library).

Missing files added.
News entry added.
Revert changeset 6661a8154eb3: Issue #3329: Add new APIs to customize memory allocators

The new API require more discussion.
Merge heads
Fix markup of the synopsis along with changing to state what is in the
module and not as a definition of what an enumeration is.
Issue #17907: touch up the code for imp.new_module().
Make it more obvious what things used in imp are snuck in through private APIs
Issue #18194: Introduce importlib.util.cache_from_source() and
source_from_cache(), finishing the work introduced in changset
4134:9cacdb9d0c59.
Move something to the right section of What's New
Issue #17177: Update the programming FAQ to use importlib
make test more robust under Windows
Issue #17177: stop using imp for compileall.
Issue #17177: Stop using imp in distutils
Issue #17177: Stop using imp in multiprocessing
Fix typo; clarify that the methods were removed entirely