1) When a breakpoint is set via a function name:
- the breakpoint gets the lineno of the def statement
- a new funcname attribute is attached to the breakpoint

2) bdb.effective() calls new function checkfuncname() to handle:
- def statement is executed: don't break.
- a first executable line of a function with a breakpoint on the lineno of the
def statement is reached: break.

This fixes bugs 976878, 926369 and 875404. Thanks Ilya Sandler.