C++ Network Library Code

Merged branches/http_integration-r72 and branches/docs-r78.

Fixed typo at end of http.qbk file.

Update documentation about tags/directives; Updated http::client.

- Cleaned up http_test_server, using boost::filesystem
- http_test_server now grants execute permissions to all files in cgi-bin/
- Tested localhost_tests.cpp with Python 2.6 and removed exclusion of test case that now works.

Changes:
- 'Content-Type' instead of 'Content-type' set by http::client
- http::client forward declaration
- Change to set the executable flags of the files that need to be executable in the server/cgi-bin directory

- Removed separate tag/traits impl for URI
- uri_fwd.hpp now uses tags from network/message
- Note: These tags/traits should probably be moved up into the root moving forward

Refactored boost::network::uri so that it's more aligned with boost::network::message; added tags and traits; added unit test.

- First stab at URI class

Created branch for URI processing

Added useful tools for managing releases.