Make child process errors kill gyp when parallel processing is on.

Make Ctrl+C kill gyp when parallel processing is on.

Manually tested these cases:
* Normal success case
* Ctrl+C during input file processing
* Syntax error in input file
* Ctrl+C during ninja generation
* Bug in Python code in ninja generation

Solution to Ctrl+C adapted from John Reese's solution here:
http://stackoverflow.com/questions/1408356/keyboard-interrupts-with-pythons-multiprocessing-pool

[scottmg, 2012-10-09 18:12:54]

Would it maybe be better to handle the children failing/exiting instead so that
syntax errors in gyp get handled too? (Or is that an unrelated problem?)

https://codereview.chromium.org/11098023/diff/1/pylib/gyp/generator/ninja.py
File pylib/gyp/generator/ninja.py (right):

https://codereview.chromium.org/11098023/diff/1/pylib/gyp/generator/ninja.py#...
pylib/gyp/generator/ninja.py:1755: signal.signal(signal.SIGINT, signal.SIG_IGN)
is this going to break ctrl-c in non-parallel?

[dmazzoni, 2012-10-09 18:40:15]

On 2012/10/09 18:12:54, scottmg wrote:
> Would it maybe be better to handle the children failing/exiting instead so
that
> syntax errors in gyp get handled too? (Or is that an unrelated problem?)

Only halfway related, but I went ahead and fixed that too. Take another look.

https://codereview.chromium.org/11098023/diff/1/pylib/gyp/generator/ninja.py
> File pylib/gyp/generator/ninja.py (right):
> 
>
https://codereview.chromium.org/11098023/diff/1/pylib/gyp/generator/ninja.py#...
> pylib/gyp/generator/ninja.py:1755: signal.signal(signal.SIGINT,
signal.SIG_IGN)
> is this going to break ctrl-c in non-parallel?

No, I'm only calling this in a method that's only called in child processes.

[scottmg, 2012-10-09 18:44:08]

lgtm