Fix rebuilding programs after context loss

Uniform state needs to be reinitialized after context loss occurs.

Fixes a regression introduced by commit "Cache shader program uniform
state to avoid redundant uniform1i calls".
Merge pull request #313 from NVIDIA/fix-rebuilding-programs

Fix rebuilding programs after context loss
Merge branch 'V3.1' of https://github.com/xeolabs/scenejs into luke
new build