readfile and textxform functions do not rely on 4k limit anymore

From kacfengine/core-4k-limit
If the user has passed "0" or "inf" to the function, then maxsize should be set to 0, so that the internal ```CfReadFile()``` function reads with no limit. No need to exit in case of ```maxsize>CF_INFINITY```, 

```CF_INFINITY``` is just a magic number meaning the user used "inf" in the policy. It should not be used as a buffer size, it's just an arbitrary number.