OpenSSL and thread support

[Matt Van Mater <matt_(_dot_)_vanmater_(_at_)_gmail_(_dot_)_com>]

I'm playing around with a reverse proxy app called Pound that requires
threading support in OpenSSL, but apparently the version of OpenSSL in
the source tree does not enable threading by default.

Is there a reason why I shouldn't enable threading in a stand alone
version of OpenSSL?  Is there a performance reason, vulnerability, or
some other nasty side effect associated with threading support that I
should be aware of?  Obviously I don't want to introduce any problems
by messing with this.

Matt