Please add package version and variant info to `make.log`

[lemzwerg (Werner Lemberg)]

I've noticed that in main.log files there is no information what version and variants have been requested – for example,

  ImageMagick @6.9.9-40_7+x11

I suggest to make port add this information at the very top of main.log. This would also help identify various make.log files more easily.