Implement appending to standard man(7) and mdoc(7) macros with .am.

With roff_getstrn(), provide finer control which definitions
can be used for what:
* All definitions can be used for .if d tests and .am appending.
* User-defined for \* expansion, .dei expansion, and macro calling.
* Predefined for \* expansion.
* Standard macros, original or renamed, for macro calling.

Several related improvements while here:
* Do not return string table entries that have explicitly been removed.
* Do not create a rentab entry when trying to rename a non-existent macro.
* Clear an existing rentab entry when the external interface
roff_setstr() is called with its name.
* Avoid trailing blanks in macro lines generated from renamed
and from aliased macros.
* Delete the duplicate __m*_reserved[] tables, just use roff_name[].

3 files changed, 41 insertions, 0 deletions

diff --git a/regress/roff/rn/Makefile b/regress/roff/rn/Makefile
new file mode 100644
index 00000000..87ef7fe1
--- /dev/null
+++ b/regress/roff/rn/Makefile
@@ -0,0 +1,5 @@
+# $OpenBSD: Makefile,v 1.10 2017/03/07 20:00:02 schwarze Exp $
+
+REGRESS_TARGETS	 = append
+
+.include <bsd.regress.mk>
diff --git a/regress/roff/rn/append.in b/regress/roff/rn/append.in
new file mode 100644
index 00000000..5ae2cfb1
--- /dev/null
+++ b/regress/roff/rn/append.in
@@ -0,0 +1,23 @@
+.Dd June 18, 2017
+.Dt RN-APPEND 1
+.Os OpenBSD
+.Sh NAME
+.Nm rn-append
+.Nd append to renamed standard macro
+.Sh DESCRIPTION
+original macro:
+.Bo in brackets
+.Bc
+.Pp
+renamed macro:
+.rn Bc myBc
+.Bo in brackets
+.myBc
+.Pp
+appending to macro:
+.am myBc
+.Pq appended words
+..
+.Bo more in brackets
+.myBc
+final text
diff --git a/regress/roff/rn/append.out_ascii b/regress/roff/rn/append.out_ascii
new file mode 100644
index 00000000..99b61d79
--- /dev/null
+++ b/regress/roff/rn/append.out_ascii
@@ -0,0 +1,13 @@
+RN-APPEND(1)                General Commands Manual               RN-APPEND(1)
+
+NNAAMMEE
+     rrnn--aappppeenndd - append to renamed standard macro
+
+DDEESSCCRRIIPPTTIIOONN
+     original macro: [in brackets]
+
+     renamed macro: [in brackets]
+
+     appending to macro: [more in brackets] (appended words) final text
+
+OpenBSD                          June 18, 2017                         OpenBSD