and vice versa"
Initial import of the dtoa.c code and custom wrappers around it to allow
its usage from the server code.

Conversion of FLOAT/DOUBLE values to DECIMAL ones or strings and vice
versa has been significantly reworked. As the new algoritms are more
precise than the older ones, results of such conversions may not always
match those obtained from older server versions. This in turn may break
compatibility for some applications.

This patch also fixes the following bugs:
- bug #12860 "Difference in zero padding of exponent between Unix and
Windows"
- bug #21497 "DOUBLE truncated to unusable value"
- bug #26788 "mysqld (debug) aborts when inserting specific numbers into
char fields"
- bug #24541 "Data truncated..." on decimal type columns without any
good reason"