vs2013 got strtoll/strtoull
Fixed a bug which made the MySQL backend mistake an escaped single quote inside
a string literal for the closing quote. This resulted in incorrect behavior
if the same string literal contained a colon character ':'.
Merge pull request #217 from fly2xj/master

Fix compilation with MSVS 2013 which now defines strtoll/strtoull in its headers.
Special case := (assignment operator) when parsing the query (MySQL).
Merge github.com:SOCI/soci into SOCI-master