libdpkg: Rename database module to pkg-db

This matches the namespace for the provided functions, and disambiguates
what kind of database it's refering to.

lib/dpkg/Makefile.am

@@ -28,7 +28,6 @@ libdpkg_a_SOURCES = \
 	cleanup.c \
 	command.c \
 	compress.c \
-	database.c \
 	dbmodify.c \
 	debug.c \
 	dir.c \
@@ -49,6 +48,7 @@ libdpkg_a_SOURCES = \
 	parsehelp.c \
 	path.c \
 	pkg.c \
+	pkg-db.c \
 	pkg-array.c \
 	pkg-format.c \
 	pkg-list.c \

lib/dpkg/database.c

@@ -1,6 +1,6 @@
 /*
  * libdpkg - Debian packaging suite library routines
- * dpkg-db.h - Low level package database routines (hash tables, etc.)
+ * pkg-db.c - Low level package database routines (hash tables, etc.)
  *
  * Copyright © 1995 Ian Jackson <ian@chiark.greenend.org.uk>
  *