[with spkg, positive review] fix Macaulay2 building

[malb]

I've uploaded a new SPKG for M2 to:

 http://sage.math.washington.edu/home/malb/spkgs/macaulay2-1.1-r7210.p1.spkg

which fixes a couple of compilation problems:

• UNAME might not be defined
• some standard headers are not included in overflow.hpp

[mabshoff]

Positive review. A couple remarks:

• The fixes malb did should go upstream.
• I fixed the boehm_gc and gdbm detection code since it only works for default spkgs and not optional ones - my bad.

Cheers,

Michael

[mabshoff]

Oops, I forgot to mention that the updated spkg is at

 http://sage.math.washington.edu/home/mabshoff/release-cycles-3.1.2/alpha1/macaulay2-1.1-r7210.p1.spkg

Cheers,

Michael

[mabshoff]

Merged in Sage 3.1.2.alpha1