Change tan function test value.

Apparently there is some disagreement on the tangent of 40 between browser and node. 42 is the answer.
Prevent data-uri function from embedding files larger than 32KB.

Although IE8 does support data-uris, it only does so with a limit of 32KB. It's a silly limitation, but a source of potential bugs. When the limit is exceeded, the data-uri() function will simply return a normal url() value with a relative path to the asset.

One may pass --no-ie-compat to lessc to avoid this safeguard.
Functions use evalEnv, not parseEnv. (move ieCompat env flag)
Actually pass ieCompat into evalEnv for lessc.
Pass silent and verbose flags to evalEnv.
Wrap data-uri warnings in an env.silent check, silencing test set.
Fallback url() value for data-uri function should be quoted.
Use original node so that original seperator is used instead of the native one. Fixes unit tests on windows.