Rearrange Python breakpoint node in documentation

I noticed that the Python breakpoint documentation was ordered a bit
oddly.  It documented the constructor; then the stop method; then the
watchpoint constants (used for the constructor); then various other
methods and attributes; then the other constants used by the
constructor; and then finally some more methods and attributes.

This patch rearranges the node a little to move the constants to just
after the constructor and before the other methods and attributes.

2016-07-13  Tom Tromey  <tom@tromey.com>

	* python.texi (Breakpoints In Python): Move table of types and
	table of watchpoint types earlier in node.