[rtmpdump] Compilation on MinGW (windows) seems to be broken on r546

[pnixte at gmail.com]

Hello.

It seems that compilation on MinGW (windows) is broken on r546.
Last working version I had tested was r540.

The error is an "undefined reference to WinMain at 16" for the "librtmp" directory.
Adding an "int main() {}" line in the librtmp/rtmnp.c seems to fix the
problem for the directory but breaks "rtmpdump.exe" compilation with a
"multiple definitions of 'main'" error.

Any help?