rmthm – Use a roman font for theorem statements

Mod­i­fies the the­o­rem en­vi­ron­ment of LaTeX 2.09 to cause the state­ment of a the­o­rem to ap­pear in \rm.
LaTeX 2e users should use a more gen­eral pack­age (such as nthe­o­rem) to sup­port this re­quire­ment.