main.c: Fixed compiling on MinGW-w64.
tests/run-px: Don't override SYSTEM_WGETRC and WGETRC to /dev/null if it is already set.

This makes test suite pass on Wine because Wine blocks /dev/null.
(Maybe we could invent some way to use nul instead of /dev/null on Windows/Wine,
 see http://stackoverflow.com/questions/313111/dev-null-in-windows)
.travis.yml: Initial commit.
.travis.yml: Added comment for unsupported build flags.