In the FLOAT/DOUBLE to string conversions a class global string was used
to store the result. Unfortunately it is possible for an instance of
this class to be used by multiple threads of PrimProc simultaneously.
This would cause a race and data corruption or more likely a crash.
This fix passes a string object from the caller to use instead.
For the initial BLOB/TEXT pull request we put them in the same bucket as
VARBINARY, forcing many functions to be disabled. This patch enables the
same TEXT function support as VARCHAR.
