git-p4: honor --changesfile option and test

When an explicit list of changes is given, it makes no sense to
use @all or @3,5 or any of the other p4 revision specifiers.
Make the code notice when this happens, instead of just ignoring
--changesfile.  Test it.

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/fast-import/git-p4

@@ -2024,6 +2024,17 @@ class P4Sync(Command, P4UserMap):
         revision = ""
         self.users = {}
 
+        # Make sure no revision specifiers are used when --changesfile
+        # is specified.
+        bad_changesfile = False
+        if len(self.changesFile) > 0:
+            for p in self.depotPaths:
+                if p.find("@") >= 0 or p.find("#") >= 0:
+                    bad_changesfile = True
+                    break
+        if bad_changesfile:
+            die("Option --changesfile is incompatible with revision specifiers")
+
         newPaths = []
         for p in self.depotPaths:
             if p.find("@") != -1:
@@ -2040,7 +2051,10 @@ class P4Sync(Command, P4UserMap):
                 revision = p[hashIdx:]
                 p = p[:hashIdx]
             elif self.previousDepotPaths == []:
-                revision = "#head"
+                # pay attention to changesfile, if given, else import
+                # the entire p4 tree at the head revision
+                if len(self.changesFile) == 0:
+                    revision = "#head"
 
             p = re.sub ("\.\.\.$", "", p)
             if not p.endswith("/"):