pudb takes a long time to display GUI, taking 100% CPU

I am working with a pretty big code base and when hitting a pudb.set_trace() the thread goes to 100% CPU and stays there for almost one and a half minute before the pudb GUI shows up. Once when I interrupted it because I was tired of waiting I got this traceback:

```
Traceback (most recent call last):
File "/usr/lib64/python2.7/runpy.py", line 162, in _run_module_as_main
"__main__", fname, loader, pkg_name)
File "/usr/lib64/python2.7/runpy.py", line 72, in _run_code
exec code in run_globals
File "/home/andersh/env_resolve/lib/python2.7/site-packages/pudb-2012.2-py2.7.egg/pudb/__main__.py", line 3, in
main()
File "/home/andersh/env_resolve/lib/python2.7/site-packages/pudb-2012.2-py2.7.egg/pudb/run.py", line 30, in main
steal_output=options.steal_output)
File "/home/andersh/env_resolve/lib/python2.7/site-packages/pudb-2012.2-py2.7.egg/pudb/__init__.py", line 48, in runscript
for bpoint_descr in load_breakpoints(dbg):
File "/home/andersh/env_resolve/lib/python2.7/site-packages/pudb-2012.2-py2.7.egg/pudb/settings.py", line 389, in load_breakpoints
return parse_breakpoints(lines)
File "/home/andersh/env_resolve/lib/python2.7/site-packages/pudb-2012.2-py2.7.egg/pudb/settings.py", line 362, in parse_breakpoints
if get_breakpoint_invalid_reason(filename, lineno) is None:
File "/home/andersh/env_resolve/lib/python2.7/site-packages/pudb-2012.2-py2.7.egg/pudb/lowlevel.py", line 41, in get_breakpoint_invalid_reason
if lineno not in get_executable_lines_for_file(filename):
File "/home/andersh/env_resolve/lib/python2.7/site-packages/pudb-2012.2-py2.7.egg/pudb/lowlevel.py", line 16, in get_executable_lines_for_file
codes = [compile("".join(getlines(filename)), filename, "exec")]
KeyboardInterrupt
```

Start in pudb/settings.py at load_breakpoints and parse_breakpoints, then follow the call into pudb/lowlevel.py's get_executable_lines_for_file shown in the traceback. Reproduce the delay with a large Python codebase and inspect the breakpoint-loading path. Done means pudb's GUI opens without the prolonged 100% CPU wait, with coverage for the reported case if the repository's tests support it.

Written by the indexing model from the issue text.