Make secp256k1_ge_set_gej work with the point at infinity
Merge pull request #62

1136bed Make secp256k1_ge_set_gej work with the point at infinity (Pieter Wuille)
Split up signing and verification initialization
Set precomputation table late and unset early.

Set the global pointer to the precomputation table only after initializing
it completely, and unset it before doing any uninitialization.

This causes fail-fast behavior in case of race conditions between
initialization and operations using it.