This reverts commit 6476cf3c, reversing
changes made to 0186b90b.

Appveyor: compile with Mingw32 GCC 4.9.3

Let use an old GCC to compile SRB2

See merge request !112

Netcode shit

*takes the cookie*

-Added a timeout for game state downloading to prevent definitive join freezes in some cases. The timeout has a minimum value of "jointimeout" and gets higher as the game state grows in size
-If the server tries to kick a joiner who is downloading the game state, they will get a timeout instead, because a regular kick would only happen once the game state has been downloaded
-Added a timeout for player ticcmd packets, again to prevent freezes to happen in some cases
-File/game state downloading is now faster, the speed is controlled by the "downloadspeed" cvar, in packets per tic
-The reason is now properly shown when the server refuses connection
-Changed the default values of "nettimeout" to 10 seconds (previously 15) and "maxsend" to 4 MB (previously 1)
-Added a "noticedownload" cvar that displays a message in the server console when someone is downloading a file

CMake: Fix nasm Linux builds

When compiling under Linux with CMake and nasm/yasm enabled, the operation would fail during linking with undefined symbols related to the tmap files.
This commit adds support for passing flags to the assembler and passes ```-DLINUX``` in order to compile.

After this change, binaries are successfully compiled with either nasm or yasm on Linux systems.
Tested on Ubuntu.

See merge request !153

CMake: split inline ASM code from vid_copy.s code

See merge request !151

Update Code::Block project

See merge request !145

Remove secplanes

This is just removing SSNTails's old port of ZDoom's secplane code and math, from back when he attempted slopes himself. The slopes we've had since 2.1.15 however do not need these, so we can pretty much toss the code for them out now (nothing uses them anyway).

See merge request !149

Netcode shit

Remove all traces of SSN's old port of ZDoom's secplanes for slopes, since our slopes do not need them