[UPDATE] minor enhancement

[UPDATE] retrieve SoapHeader namespace and add it to the operation php
doc
[UPDATE] bug fix, add cases and improve php doc

[UPDATE] bug fix, add test cases and improve php doc
Fix location determination from import tags when path is relative with
"../"
Improve php doc to indicate if SOAPHeader(s) is/are required, by default
SOAPHeader(s) is/are considered as required unless the "required"
attribute specifies the opposite
Add several test cases for SOAPHeaders and others