Losing a TCP SYN requires a long painful (typically 3 second) delay
before being retried. This patch creates a second parallel connection
attempt for any nsHttpConnection which has not become writable before
a timeout occurs.
If you assume .5% packet loss, this converts a full 3 second delay
from a 1 in 200 event into a 1 in 40,000 event.
Whichever connection establishes itself first is used. If another one
has been started and it does connect before the one being used is
closed then the extra one is handed to the connection manager for use
by a different transaction - essentially a persistent connection with
0 previous transactions on it. (Another way to think about is
pre-fetching a 3WHS on a high latency connection).
The pref network.http.connection-retry-timeout controls the amount of
time in ms to wait for success on the initial connection before beginning
the second one. Setting it to 0 disables the parallel connection, the
default is 250.
