Testability improvements

Added a utility function to report errors, and use it in unit tests.
Also add another ENV option (SFDC_URL) to  easily change the salesforce
instance to unit test against.
Report error details for failed tests

Use reportFailureDetails() for all failing tests, to report the
failure reason and code.
add a default for convertedStatus, add more tests
add web proxy, bump version
add proxy support, bump version
updated Changes file to reflect 0.19
Merge branch 'master' of https://github.com/dclendenan/WWW-Salesforce

Resolved conflicts in:
	t/WWW-Salesforce.t
Improve version-diag details, remove default convertedStatus

Remove unwanrted default for convertLead added in interim commit
Add more details to the diag for which versions we're testing