context: make warning message for hidden revision extensible
Extensions might want to create new filternames and change what revisions
are considered hidden or shown. This is the case for inhibit that enables
direct access to hidden hashes with the visible-directaccess-nowarn filtername.
By using startswith instead of a direct comparison with 'visible' we
allow extensions to do that and not work directly on the 'visible' filtername
used by core.
$ hg init
$ cat > a <<EOF
> a
> b
> c
> EOF
$ hg ci -Am adda
adding a
$ cat > a <<EOF
> d
> e
> f
> EOF
$ hg ci -m moda
$ hg diff --reverse -r0 -r1
diff -r 2855cdcfcbb7 -r 8e1805a3cf6e a
--- a/a Thu Jan 01 00:00:00 1970 +0000
+++ b/a Thu Jan 01 00:00:00 1970 +0000
@@ -1,3 +1,3 @@
-d
-e
-f
+a
+b
+c
$ cat >> a <<EOF
> g
> h
> EOF
$ hg diff --reverse --nodates
diff -r 2855cdcfcbb7 a
--- a/a
+++ b/a
@@ -1,5 +1,3 @@
d
e
f
-g
-h
should show removed file 'a' as being added
$ hg revert a
$ hg rm a
$ hg diff --reverse --nodates a
diff -r 2855cdcfcbb7 a
--- /dev/null
+++ b/a
@@ -0,0 +1,3 @@
+d
+e
+f
should show added file 'b' as being removed
$ echo b >> b
$ hg add b
$ hg diff --reverse --nodates b
diff -r 2855cdcfcbb7 b
--- a/b
+++ /dev/null
@@ -1,1 +0,0 @@
-b