Let roff_getname() end the roff identifier at a tab character

and audit all its callers whether termination is handled correctly.

Resulting improvements:
* An escape or tab ending the macro name in a macro invocation
is discarded, and argument processing is started after it.
* An escape or tab ending a name in ".if d" and ".if r" is preserved.
* An escape ending a name in ".ds" causes the whole request to be ignored.
* A tab ending a name in ".ds" becomes part of the string.
* An escape or tab ending a name in ".rm"
causes the rest of the line to be ignored.
* An escape or tab ending the first name in ".als", ".rn", or ".nr"
causes the whole request to be ignored.

Kurt Jaeger <pi at FreeBSD> made me aware of
  https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=235456#c0
and in that bug report, comment 0 item (3) is a special case
of this class of issues.

Yes, the "mh" manual pages are no doubt among the worst on the planet.

1 files changed, 15 insertions, 0 deletions

diff --git a/regress/roff/rn/tab.out_ascii b/regress/roff/rn/tab.out_ascii
new file mode 100644
index 00000000..6f00c8c1
--- /dev/null
+++ b/regress/roff/rn/tab.out_ascii
@@ -0,0 +1,15 @@
+RN-TAB(1)                   General Commands Manual                  RN-TAB(1)
+
+NNAAMMEE
+     rrnn--ttaabb - tab characters in macro renaming requests
+
+DDEESSCCRRIIPPTTIIOONN
+     trying to rename with a tab between the names:
+     calling the macro with the old name: testval
+     calling the macro with the new name:
+
+     trying to rename with a tab after the names:
+     calling the macro with the old name:
+     calling the macro with the new name: testval
+
+OpenBSD                        February 6, 2019                        OpenBSD