runtests.pl: check for tstunnel command on Windows

The Windows console version of stunnel is called "tstunnel", while
running "stunnel" on Windows spawns a new console window which
cannot be handled by the testsuite.
examples: Added IMAP SSL and TLS examples
examples: Added SMTP SSL example
examples: Reworked POP3 examples for additional upcoming POP3 examples
runtests.pl: Updated copyright year after edit from d718abd968aeb4
examples: Added return of error code in POP3 examples
examples: Added POP3 RETR example
examples: Added POP3 UIDL example
examples: Added POP3 DELE example
examples: Added POP3 TOP example
examples: Added POP3 STAT example
pop3-stat.c: Corrected small typo from commit 91d62e9abd761c
examples: Added POP3 NOOP example
examples: Added IMAP NOOP example
examples: Added POP3 TLS example
Examples: Renamed SMTP MAIL example to match other email examples
multi.c: fix possible dereference of null pointer
packages: follow up fix for a47c142, 11e8066 and 92b9ae5
docs/INTERNALS: follow up fix for 11e8066 and 92b9ae5
Makefile: Added missing WinSSL and x64 configurations