Fix pythonNumberError patterns to exclude legitimate identifiers.

 * "_0" is a valid identifier!

syntax/python.vim

 
   syn match   pythonNumberError	"\<\d[_0-9]*\D\>" display
   syn match   pythonNumberError	"\<0[_0-9]\+\>" display
-  syn match   pythonNumberError	"\<\%(_[_0-9]\+\|[_0-9]\+_\)\>" display
+  syn match   pythonNumberError	"\<\d[_0-9]*_\>" display
   syn match   pythonNumber	"\<\d\>" display
   syn match   pythonNumber	"\<[1-9][_0-9]*\d\>" display
   syn match   pythonNumber	"\<\d[jJ]\>" display

test.py

 # Erroneous numbers
 
 077 100L 0xfffffffL 0L 08 0xk 0x 0b102 0o78 0o123LaB
-0_ 0_1 _0 0_x1f 0x1f_ 0_b77 0b77_ ._2 .2_ 1_j
+0_ 0_1 0_x1f 0x1f_ 0_b77 0b77_ .2_ 1_j
 
 # Strings