Expose and document rpmdb --verifydb operation

After years of BDB, sometimes folks just want some assurance that their db
is still fine. Properly exposing an operation to do so hopefully makes
less likely to poke at the db directly (with eg sqlite3 command).

(cherry picked from commit 173b737)

docs/man/rpmdb.8.md

@@ -14,6 +14,8 @@ SYNOPSIS
 
 **rpmdb** {**\--initdb\|\--rebuilddb**}
 
+**rpmdb** {**\--verifydb}
+
 **rpmdb** {**\--exportdb\|\--importdb**}
 
 DESCRIPTION
@@ -28,6 +30,8 @@ Use **\--initdb** to create a new database if one doesn\'t already exist
 (existing database is not overwritten), use **\--rebuilddb** to rebuild
 the database indices from the installed package headers.
 
+**\--verifydb** performs a low-level integrity check on the database.
+
 **\--exportdb** exports the database in header-list format, suitable
 for transfporting to another host or database type.
 

rpmdb.c

@@ -23,8 +23,8 @@ static struct poptOption dbOptsTable[] = {
     { "rebuilddb", '\0', (POPT_ARG_VAL|POPT_ARGFLAG_OR), &mode, MODE_REBUILDDB,
 	N_("rebuild database inverted lists from installed package headers"),
 	NULL},
-    { "verifydb", '\0', (POPT_ARG_VAL|POPT_ARGFLAG_OR|POPT_ARGFLAG_DOC_HIDDEN),
-	&mode, MODE_VERIFYDB, N_("verify database files"), NULL},
+    { "verifydb", '\0', (POPT_ARG_VAL|POPT_ARGFLAG_OR),
+	&mode, MODE_VERIFYDB, N_("verify database"), NULL},
     { "salvagedb", '\0', (POPT_ARG_VAL|POPT_ARGFLAG_OR|POPT_ARGFLAG_DOC_HIDDEN),
 	&mode, MODE_SALVAGEDB, N_("salvage database"), NULL},
     { "exportdb", '\0', (POPT_ARG_VAL|POPT_ARGFLAG_OR), &mode, MODE_EXPORTDB,