Linux dedicated server changes for Left4Dead

There have been many changes, enhancements, and optimizations with the
dedicated server for Linux:

* All of the code is now being compiled with gcc 4.3.0 and glibc 2.8-8
  in order to take advantage of compiler fixes and optimization
  enhancements. In order to run the l4d Linux dedicated server, you
  will need a system which can run binaries built against this version
  of glibc.

* As a performance enhancement, the dedicated server can now use the
  hardware "RDTSC" timer instead of gettimeofday() for its internal
  timing, on systems which support it ( such systems are identified by
  having the "constant_tsc" flag set in /proc/cpuinfo ). When the code
  detects that the system has this, it will execute a benchmark to
  measure the actual rate of the hardware timer, and use this for all
  timing. If this causes trouble on a system, you can set the
  environment variable "RDTSC_FREQUENCY" to "disabled".

* The Linux dedicated server is now capable of running multiple
  server instances as sub-processes off of one parent process. This
  provides a memory savings (through sharing of read-only data), a
  speedup when starting multiple servers, and also enhances server
  stability by having the servers restart as new sub-processes after
  each game is completed. This is controlled by the "-fork n" option.
  For instance, you can run "srcds_run -fork 5" to start up 5 separate
  server instances in this mode.

* When -fork mode is enabled, some options on the command line can be
  parametrized based upon the server instance, by typing '##' on the
  launching line. For instance, "-fork 10 -netconport 90##" would
  cause the first server instance to use port 9001, the second to use
  9002, etc.


* There is a new remote access feature which allows a server
  administrator (or tool) to create a persistent connection to a
  running server, and to see its entire console output and send it
  commands. This feature is enabled by using the "-netconport" option
  when launching srcds_i486. For instance, if a server is started with
  "-netconport 9000", someone with access to port 9000 of the server
  could type "telnet xxxx 9000" and view the console output. This
  feature is disabled by default, and should only be used when an
  appropriate firewall/tunnel is used to control access to this
  port. Multiple clients can connect to the netconport of a running
  server at the same time.

* If the netconsole is enabled, and the option "-netconpassword xxx"
  is set, the network console will not execute commands received
  through the netconport until the command "PASS xxx" is entered.

srcds.exe -game left4dead -ip xxx.xx.xx -port 27015 +map l4d_hospital01_apartment

srcds_run -game left4dead -ip xxx.xx.xx -port 27015 +map l4d_hospital01_apartment