Grow the string buffer at a mildly exponential rate for the getc version of get_line.  This makes test_bufio finish in 1.7 seconds instead of 57 seconds on my machine (with Py_DEBUG defined).
Grow the string buffer at a mildly exponential rate for the getc version
of get_line.  This makes test_bufio finish in 1.7 seconds instead of 57
seconds on my machine (with Py_DEBUG defined).

Also, rename the local variables n1 and n2 to used_v_size and
total_v_size.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator