[unpackfs] Allow naming a non-directory for single files

- this enables renaming files on copy

src/modules/unpackfs/main.py

@@ -58,9 +58,9 @@ class UnpackEntry:
         @p sourcefs is a type indication; "file" is special, as is
             "squashfs".
         @p destination is where the files from the source go. This is
-            **already** prefixed by rootMountPoint, so should be a 
+            **already** prefixed by rootMountPoint, so should be a
             valid absolute path within the host system.
-            
+
         The members copied and total are filled in by the copying process.
         """
         self.source = source
@@ -390,7 +390,7 @@ def run():
         sourcefs = entry["sourcefs"]
         destination = os.path.abspath(root_mount_point + entry["destination"])
 
-        if not os.path.isdir(destination):
+        if not os.path.isdir(destination) and sourcefs != "file":
             utils.warning(("The destination \"{}\" in the target system is not a directory").format(destination))
             if is_first:
                 return (_("Bad unsquash configuration"),

src/modules/unpackfs/unpackfs.conf

@@ -60,8 +60,13 @@
 #    -   source: ../src/modules/dummycpp
 #        sourcefs: file
 #        destination: "/tmp/derp"
+#
+# The *destination* and *source* are handed off to rsync, so the semantics
+# of trailing slashes apply. In order to *rename* a file as it is
+# copied, specify one single file (e.g. CHANGES) and a full pathname
+# for its destination name, as in the example below.
 
 unpack:
     -   source: ../CHANGES
         sourcefs: file
-        destination: "/tmp"
+        destination: "/tmp/changes.txt"