use autoconf macro to check for pkg-config (closes #15506)

--HG--
branch : 3.4
extra : source : 54939f3c1e176cdfd25cd12b779e36c7997ffb5a
merge 3.4 (#15506)
Issue #23015: Improved testing of the uuid module.

--HG--
branch : 3.4
Issue #23015: Improved testing of the uuid module.
Issue #22777: Test pickling with all protocols.

--HG--
branch : 3.4
Issue #22777: Test pickling with all protocols.
remove extra ssl imports (closes #23053)

Patch from Jan Matejek.

--HG--
branch : 3.4
extra : source : ebe8917189a33433084ac96ccb4e4680de34a137
merge 3.4 (#23053)
asyncio doc: call_soon() does not call immediatly the callback. Patch written
by Martin Panter.

--HG--
branch : 3.4
Merge 3.4 (asyncio doc)
Update Python/importlib.h
Update Tcl/Tk to 8.6.3

- new file dialogs on Vista+
- tclWinTime.c was cleaned up a bit, and no
  longer uses 'timezone' (which is now _timezone
  in VS2015, so we get to avoid patching that
  file).
- rules.vc is patched in both Tcl and Tk sources
  to allow building with VS2015
Fetch new external sources on the buildbots
Backed out changeset ceaac3d483a1 (buildbots refreshed)
Add NEWS item for Windows Tcl/Tk update.
Issue #21740: Fix module name in NEWS entry.
Removes bdist_wininst dependency on MFC.
Make bdist_wininst build only on demand

--HG--
rename : PCbuild/bdist_wininst.vcxproj => PC/bdist_wininst/bdist_wininst.vcxproj
rename : PCbuild/bdist_wininst.vcxproj.filters => PC/bdist_wininst/bdist_wininst.vcxproj.filters