bn_exp.c: fix x86_64-specific crash with one-word modulus.

PR: #3397
e_os.h: limit _MSC_VER trickery to older compilers.

PR: #3390
Close a whole bunch of documentation-related tickets:
    298 424 656 882 939 1630 1807 2263 2294 2311 2424 2623
    2637 2686 2697 2921 2922 2940 3055 3112 3156 3177 3277
Merge branch 'rsalz-docfixes'
RT3408; fix some (not all suggested) typo's in openssl.cnf
RT 1638; EVP_*Final() should mention they no longer cleanup the ctx.
Close 3170, remove reference to Ariel Glenn's old 0.9.8 doc
Update ticket callback docs.
Remove all RFC5878 code.

Remove RFC5878 code. It is no longer needed for CT and has numerous bugs
typo
(cherry picked from commit 2cfbec1caea8f9567bdff85d33d22481f2afb40a)
test/testutil.h test registry macros

These help standardize the structure of main() and result reporting.
Use testutil registry macros in heartbeat_test