Issue #18345: Added cookbook example illustrating handler customisation.
Closes #18345: Merged documentation update from 3.3.
Issue #15663: Revert OS X installer built-in Tcl/Tk support for 3.3.3.
Some third-party projects, such as matplotlib and PIL/Pillow,
depended on being able to build with Tcl and Tk frameworks in
/Library/Frameworks.  They were unable to build with the built-in
Tcl/Tk and/or execute correctly.
Issue #15663: merge build-installer.py changes