test-hgweb-diffs: partially adapt for Windows

Since chmod isn't supported on Windows (or vfat), I'm importing a here-doc
instead (<<EOF ..).

Option --bypass on import of the here-doc is required on Windows (or vfat) to
bypass the working directory (see hg help import). Not using --bypass would
lose the mode changing bits.

I've had to insert a --bypass on the preexisting import call futher down in the
test, because importing a patch with --exact and mode changes will fail on
Windows (and vfat).

As the point of this test is not to test commit, I'm using the import
procedure for all platforms unconditionally, that is, I'm intentionally not
keeping the original sequence of hg and chmod calls for platforms that support
exec either, which saves us having to insert an #if exec ... #else ... #endif.

tests/test-hgweb-diffs.t

@@ -1,4 +1,4 b''
-  $ "$TESTDIR/hghave" serve execbit || exit 80
+  $ "$TESTDIR/hghave" serve || exit 80
 
 setting up repo
 
@@ -12,9 +12,22 b' setting up repo'
 
 change permissions for git diffs
 
-  $ chmod +x a
-  $ hg rm b
-  $ hg ci -Amb
+  $ hg import -q --bypass - <<EOF
+  > # HG changeset patch
+  > # User test
+  > # Date 0 0
+  > b
+  > 
+  > diff --git a/a b/a
+  > old mode 100644
+  > new mode 100755
+  > diff --git a/b b/b
+  > deleted file mode 100644
+  > --- a/b
+  > +++ /dev/null
+  > @@ -1,1 +0,0 @@
+  > -b
+  > EOF
 
 set up hgweb
 
@@ -548,7 +561,7 b' test import rev as raw-rev'
   updating to branch default
   2 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ cd test1
-  $ hg import -q --exact http://localhost:$HGPORT/rev/1
+  $ hg import -q --bypass --exact http://localhost:$HGPORT/rev/1
 
 raw revision with diff block numbers