Add <cstdlib> include for srand()/rand(), and <unistd.h> for open() etc.
Include <unistd.h> on Windows if using MinGW. Disable MeteorScorer on
Windows, since it doesn't have fork() and pipe().
This is one of those little chores in managing a long-lived C++
project: standard C headers like stdio.h and math.h now have their own
place in the C++ standard as resp. cstdio, cmath, and so on. In this
branch the #include names are updated for the mert/ subdirectory; more
branches to follow.
C++11 adds cstdint, but to support compilation with the previous
standard, that change is left for later.
