Add manpage syntax checker to 'check' target

In virtually every libssh2 release Debian's lintian catches syntax errors in
manpages. Prevent it by checking manpages as a part of testsuite.

tests/Makefile.am

@@ -7,7 +7,7 @@ ssh2_SOURCES = ssh2.c
 endif
 
 ctests = simple$(EXEEXT)
-TESTS = $(ctests)
+TESTS = $(ctests) mansyntax.sh
 if SSHD
 TESTS += ssh2.sh
 endif
@@ -15,5 +15,5 @@ check_PROGRAMS = $(ctests)
 
 TESTS_ENVIRONMENT = SSHD=$(SSHD) EXEEXT=$(EXEEXT)
 
-EXTRA_DIST = ssh2.sh
+EXTRA_DIST = ssh2.sh mansyntax.sh
 EXTRA_DIST += etc/host etc/host.pub etc/user etc/user.pub

tests/mansyntax.sh

@@ -0,0 +1,35 @@
+#!/bin/sh
+set -e
+
+# Written by Mikhail Gusarov
+#
+# Run syntax checks for all manpages in the documentation tree.
+#
+
+srcdir=${srcdir:-$PWD}
+mandir=${srcdir}/../docs
+
+#
+# Only test if suitable man is available
+#
+if ! man --help | grep -q warnings; then
+  exit 77
+fi
+
+ec=0
+
+trap "rm -f $srcdir/man3" EXIT
+
+ln -sf "$mandir" "$srcdir/man3"
+
+for manpage in $mandir/libssh2_*.*; do
+  echo "$manpage"
+  warnings=$(LANG=en_US.UTF-8 MANWIDTH=80 man -M "$srcdir" --warnings \
+    -E UTF-8 -l "$manpage" 2>&1 >/dev/null)
+  if [ -n "$warnings" ]; then
+    echo "$warnings"
+    ec=1
+  fi
+done
+
+exit $ec