Fixes to WebDriver::submitForm

Fixes two issues in the WebDriver::submitForm method:

(1) Inputs with type="password" were not being filled in.
(2) Added check that $el exists before calling getTagName() (without this the test suite would end in a fatal error)
reformatted
updated PHP to 5.3.13 as it webdriver require
Merge pull request #875 from pcairns/1.8

Fixes to WebDriver::submitForm
new docs added
added tests for Issue #875
added doc for writing tests
added doc for writing tests
added doc for writing tests
added doc for writing tests
merged #875 from 1.8
added test for stting cookies by header