[Proj] Changing Math Constants

[Micah Cochran]

This is my attempt to put the math constants into M_ namespace, and when
possible use the compiler to define those constants.

I opened  PR #387
https://github.com/OSGeo/proj.4/pull/387

This is similar to an earlier PR that I had opened.

So, I'm looking for any comments about this change.

Thank you,
Micah
-- 

*Micah Cochran*

GIS Coordinator  -  City of Athens  -  Engineering Services & Community
Development Dept.  -  Dept. of Public Works Building  -  1600 ELM ST W,
Athens, AL <http://g.co/maps/ncrp7> - geo:34.820608,-86.991474 -  p.
256-233-2224  -  f. 256-233-8791 - www.athensalabama.us
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