Build from git on Mac OS

[Friedrich Beckmann]

Hi Jeremy,

i made a change in Smake (sed->awk) and now it is possible to build from git 
directly on MacOS. 
I tried this on OSX 10.9 with macports.

The relevant commit is here: 

http://git.savannah.gnu.org/cgit/pspp.git/commit/?h=gtk3&id=f3f10d128acbc9dbfc7c6ce0d181ef4a9cf39313

The reason for the Smake change is that sed on MacOS is based on BSD and 
behaves differently. See:

http://stackoverflow.com/questions/24275070/sed-not-giving-me-correct-substitute-operation-for-newline-with-mac-difference

The problem for Smake is
        • BSD sed: always appends a newline on output, even if the input line 
doesn't end in one.

I added also a description in README.git how to build on MacOS with macports.

Cheers

Friedrich