Clarification of changelog entry.

Fixed optimisation problem with @code{DATETIME} and value outside

@code{DATETIME} range.

@item

Removed BDB documentation.

Removed Sleepycat's BDB doc files from the source tree, as they're not

needed (MySQL covers BDB in its own documentation).

@item

Fixed MIT-pthreads to compile with @code{glibc} 2.2 (needed for

@code{make dist}).