Fix for ticket #1036: Add proxy-style (absolute-url) requests support

[sjtubinlong]

Add absolute-url support as described in ticket #1036.

1. Simply parse the uri startswith 'http' or 'https' via urlparse.urlparse and convert it into relative-path
2. add several test cases in httpserver_test

[sjtubinlong]

py3.2 DEPS=true

ERROR: test_malformed_first_line (tornado.test.httpserver_test.HTTPServerRawTest)

Traceback (most recent call last):
File "/home/travis/virtualenv/python3.2.5/lib/python3.2/site-packages/tornado-4.0b1-py3.2-linux-x86_64.egg/tornado/testing.py", line 118, in call
result = self.orig_method()
File "/home/travis/virtualenv/python3.2.5/lib/python3.2/site-packages/tornado-4.0b1-py3.2-linux-x86_64.egg/tornado/test/httpserver_test.py", line 400, in test_malformed_first_line
self.wait()
File "/home/travis/virtualenv/python3.2.5/lib/python3.2/site-packages/tornado-4.0b1-py3.2-linux-x86_64.egg/tornado/testing.py", line 603, in exit
raise Exception("did not get expected log message")
Exception: did not get expected log message

Ran 1014 tests in 16.726s
FAILED (errors=1, skipped=40)
Some tests were skipped because: CaresResolver doesn't recognize fake
NXDOMAIN, PEP 380 not available, dual-stack servers often have port
conflicts on travis, localhost does not resolve to ipv6, needs fix, no
testable future imports, timing tests unreliable on travis, twisted
module not present
[E 140627 04:54:30 testing:687] FAIL

[bdarnell]

We should do something to make the rest of the parsed url available. RFC 2616 section 5.2 says that the Host header should be ignored when an absolute url is given and the host from this url should be used instead.