Rationalise and document log options somewhat.

TOOLTYPE_NONNETWORK (i.e. pterm) already has "-log" (as does Unix
PuTTY), so there's no sense suppressing the synonym "-sessionlog".

Undocumented lacunae that remain:

plink accepts -sessionlog, but does nothing with it. Arguably it should.

puttytel accepts -sshlog/-sshrawlog (and happily logs e.g. Telnet
negotiation, as does PuTTY proper).

(cherry picked from commit a454399ec8)

Conflicts:
	unix/uxplink.c
	windows/winplink.c

(cherry-picker's notes: the conflict was only contextual, in the Plink
help output)

unix/gtkwin.c

@@ -2653,7 +2653,7 @@ static void help(FILE *fp) {
 "  -ut, +ut                  Do(default) or do not update utmp\n"
 "  -ls, +ls                  Do(default) or do not make shell a login shell\n"
 "  -sb, +sb                  Do(default) or do not display a scrollbar\n"
-"  -log PATH                 Log all output to a file\n"
+"  -log PATH, -sessionlog PATH  Log all output to a file\n"
 "  -nethack                  Map numeric keypad to hjklyubn direction keys\n"
 "  -xrm RESOURCE-STRING      Set an X resource\n"
 "  -e COMMAND [ARGS...]      Execute command (consumes all remaining args)\n"

unix/uxplink.c

@@ -580,6 +580,9 @@ static void usage(void)
     printf("  -N        don't start a shell/command (SSH-2 only)\n");
     printf("  -nc host:port\n");
     printf("            open tunnel in place of session (SSH-2 only)\n");
+    printf("  -sshlog file\n");
+    printf("  -sshrawlog file\n");
+    printf("            log protocol details to a file\n");
     exit(1);
 }