Fix cygwin path in download_sdk.py.

This change should fix a lot of the broken windows buildbots.

Also, add error function.

Also, only look back 100 revision for an SDK to download.

BUG=https://code.google.com/p/naclports/issues/detail?id=63

Review URL: https://codereview.chromium.org/11975020

git-svn-id: http://naclports.googlecode.com/svn/trunk/src@663 7dad1e8b-422e-d2af-fbf5-8013b78bd812
fix nethacks build

BUG=None
TEST=make nethacks

Review URL: https://codereview.chromium.org/11886083

git-svn-id: http://naclports.googlecode.com/svn/trunk/src@664 7dad1e8b-422e-d2af-fbf5-8013b78bd812
Fix broken pnacl bots.

Remove -f/--flavor option from download_sdk.py.  It was only
needed for downloading the legacy pnacl-specific SDK which
no longer exists.

Remove redundant buildbot_sdk_setup.py.

pnacl bots now share cleanup and SDK install steps with other
bots.

BUG=None
TEST=BUILDBOT_BUILDERNAME=linux-pnacl_newlib-all build_tools/buildbot_selector.sh

Review URL: https://codereview.chromium.org/11973017

git-svn-id: http://naclports.googlecode.com/svn/trunk/src@665 7dad1e8b-422e-d2af-fbf5-8013b78bd812
Call download_sdk.py using relative path.

This should fix the win32 bots which use non-cygwin
python which can't parse an absolute cygwin path.

BUG=

Review URL: https://codereview.chromium.org/11968029

git-svn-id: http://naclports.googlecode.com/svn/trunk/src@666 7dad1e8b-422e-d2af-fbf5-8013b78bd812
Fix broken pnacl bots.

Make setting of NACLPORTS_CFLAGS/LDFLAGS universal so they
are available in pancl builds too.

BUG=None
TBR=binji
TEST=NACL_ARCH=pnacl make

Review URL: https://codereview.chromium.org/11968046

git-svn-id: http://naclports.googlecode.com/svn/trunk/src@667 7dad1e8b-422e-d2af-fbf5-8013b78bd812