In transam.h, don't expose static inline functions to frontend code.

In transam.h, don't expose static inline functions to frontend code.

That leads to unsatisfied external references if the C compiler fails
to elide unused static functions.  Apparently, we have no buildfarm
members building HEAD that have that issue ... but such compilers still
exist in the wild.  Need to do something about that.

In passing, fix Berkeley-era typo in comment.

Discussion: https://postgr.es/m/27054.1558533367@sss.pgh.pa.us