Rewrite mul/sqr for 32bit/64bit

- interleave calculation of the lower and upper partial product ranges, and reduction
- less registers needed, more opportunities for parallel ops
Add equalities relating input and output variables
Add overflow analysis to field_5x52_int128_impl.h
Add overflow analysis to field_10x26_impl.h
Merge pull request #103

f8cce95 Add overflow analysis to field_10x26_impl.h (Pieter Wuille)
a518598 Add overflow analysis to field_5x52_int128_impl.h (Pieter Wuille)
fa0d620 Add equalities relating input and output variables (Pieter Wuille)
5dd421b Rewrite mul/sqr for 32bit/64bit (Peter Dettman)
Switch to C89 comments in prep for making the whole codebase C89 compatible.

This should be whitespace/comment only changes and should produce the same
object code.
Correct .gitignore to correctly account for build-aux.
Merge pull request #106

8ca6a9c Correct .gitignore to correctly account for build-aux. (Phillip Mienk)
Merge pull request #105

71712b2 Switch to C89 comments in prep for making the whole codebase C89 compatible. (Gregory Maxwell)
Update README.md
Merge pull request #108

6c7f0c6 Update README.md (Pieter Wuille)
Add DETERMINISTIC to avoid line number/source dependent binaries

This will make it easier to detect changes without semantic impact.
Merge pull request #107

f49b2ef Add DETERMINISTIC to avoid line number/source dependent binaries (Pieter Wuille)
Make secp256k1_eckey_pubkey_serialize fail for infinity
Test whether recovered public keys are not infinity

Fixes a bug discovered by Sergio Demian Lerner.
Add test that recovering infinity fails
Merge pull request #110

3bf029d Add test that recovering infinity fails (Pieter Wuille)
4861f83 Test whether recovered public keys are not infinity (Pieter Wuille)
bbe67d8 Make secp256k1_eckey_pubkey_serialize fail for infinity (Pieter Wuille)
build: osx: attempt to work with homebrew keg-only packages
Merge pull request #115

e2274c5 build: osx: attempt to work with homebrew keg-only packages (Cory Fields)
Don't split the g factor when not using endomorphism