Use PyFrame_GetLineNumber to get line numbers #8

The CPU profiler currently uses f_lineno as the line associated with each sample. However, f_lineno points to the start of the frame. Looking at a source listing of these profiles in pprof results in all samples appearing to be from the function definition.

One can use PyFrame_GetLineNumber (available in Python 2.7 as well) instead to get the currently-executing line from a frame. This can help understand where within a function the program is executing.