wireproto: move wireproto capabilities computation in a subfunction
It will help people that need to add capabilities (in a more subtle was that
just adding some to the list) in multiple way:
1. This function returns a list, not a string. Making it easier to look at,
extend or alter the content.
2. The original capabilities function will be store in the dictionary of wire
protocol command. So extension that wrap this function also need to update
the dictionary entry.
Both wrapping and update of the dictionary entry are needed because the
`hello` wire protocol use the function itself. This is specifically sneaky for
extension writer as ssh use the `hello` command while http use the
`capabilities` command.
With this new `_capabilities` function there is one and only one obvious
place to wrap when needed.
Test encode/decode filters
$ hg init
$ cat > .hg/hgrc <<EOF
> [encode]
> not.gz = tr [:lower:] [:upper:]
> *.gz = gzip -d
> [decode]
> not.gz = tr [:upper:] [:lower:]
> *.gz = gzip
> EOF
$ echo "this is a test" | gzip > a.gz
$ echo "this is a test" > not.gz
$ hg add *
$ hg ci -m "test"
no changes
$ hg status
$ touch *
no changes
$ hg status
check contents in repo are encoded
$ hg debugdata a.gz 0
this is a test
$ hg debugdata not.gz 0
THIS IS A TEST
check committed content was decoded
$ gunzip < a.gz
this is a test
$ cat not.gz
this is a test
$ rm *
$ hg co -C
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
check decoding of our new working dir copy
$ gunzip < a.gz
this is a test
$ cat not.gz
this is a test
check hg cat operation
$ hg cat a.gz
this is a test
$ hg cat --decode a.gz | gunzip
this is a test
$ mkdir subdir
$ cd subdir
$ hg -R .. cat ../a.gz
this is a test
$ hg -R .. cat --decode ../a.gz | gunzip
this is a test
$ cd ..