BUG: Fix for Timestamp handling in xlwt and xlsxwriter engines.
Fix for writing Timestamp objects using the xlwt and xlsxwriter
engines. Both modules write Excel dates and times using
datetime.timedelta which differs from pandas.Timedelta. This
fix coerces Timestamp objects to datetime objects.

fixes #9139.

ok, this seems ok. pls add a release note (bug fix section).
 @jreback,

I've added a release note. Note 100% sure if it is in the correct place though. That is probably something that could be added to the Contributing.md doc as some stage.

If it is wrong let me know and I'll fix it.

Rebased and updated.

John
 Release note is fine!
 see #9185. Going to steal your tests, but should work after that fix is done/merged.
 replaced by #9257 (tests only are necesssary)
