Changed proxy handling in HTTP ioslave to support multiple proxy server, i.e.
PAC script files and fix several other related issues:

* Added a new function to TCPSlaveBase that attempts to connect to the a
remote server without automatically sending error notitification to the client.

* Moved the proxy related code from 'resetSessionSettings' to 'httpOpenConnection'.
Proxy information will now only be set from 'setHost' and only be reset when
'reparseConfiguration' is invoked.

* Added a new variable to the HTTPRequest to store multiple proxy URLs.

* Modified 'httpShouldCloseConnection' to account for multiple proxy addresses.

* Modified 'sendQuery' to connect to the remote server before formatting the HTTP
headers so that the headers properly reflect the correct proxy settings.

* Removed support for 'PersistentProxyConnection' option since it serves no
other purpose than to cause unnecessary failures and bugs when using proxy
servers. To see these problems, simply disable the 'Use persistent proxy conneciton'
option in the proxy configuration dialog and use a proxy server, e.g. privoxy.

* Do not reset m_request.ikeepAlive flag in httpCloseConnection. Otherwise, it
can inadvertently set the flag to false in ::sendQuery where httpCloseConnection
might get called under certain circumstances. In general this flag should
originally be set in one location, resetSessionConfiguration, and changed
only to accomodate what the server based on its response.

* If the server sends back a "keep-alive" header, but reports itself as a
HTTP/1.0 server, make sure m_request.isKeepAlive is set to true.

REVIEW: 102696