Implement cross-platform snprintf

[willyd]

Windows does not have snprintf:

See this PR for possible implementation
BVLC#2084

Otherwise maybe we can use #define s like in gtest_all.cc

[lunzueta]

According to this discussion (http://stackoverflow.com/questions/2915672/snprintf-and-visual-studio-2010) the possible solutions to this in Windows depend on the Visual Studio version used. I guess that it is necessary to specify which would be the minimal VS version that should be used for Caffe.

Besides, I guess that MinGW should also be taken into account and not only Visual Studio, but I'm not familiar to it. Here some comments about this:
http://sourceforge.net/p/mingw-w64/mailman/message/31241434/

[bhack]

http://stackoverflow.com/questions/5847480/what-is-the-c-idiom-to-replace-snprintf3

[eelstork]

Fixed on master (see BVLC#3361)

[willyd]

Closing fixed by: BVLC#3361