Markdown Filter: Yaml and Html subfilters can produce trans-unit id collisions

[Chase Tingley]

Testcase attached. Running

tikal.sh -fc [e-mail] -x testcase.md

Produces two trans-units with the same id:

<group id="sd1_ssf1" resname="sub-filter:sd1">
<group id="sd1_sf1_sg1" resname="sd1_1">
<trans-unit id="sd1_sf1_tu1" resname="header" xml:space="preserve">
<source xml:lang="en">Hello world</source>
<target xml:lang="fr">Hello world</target>
</trans-unit>
</group>
</group>
<group id="sd1_ssf1" resname="sub-filter:sd1">
<trans-unit id="sd1_sf1_tu1" resname="sd1_2" restype="x-th" xml:space="preserve">
<source xml:lang="en">Goodbye world ...</source>
<target xml:lang="fr">Goodbye world ...</target>
</trans-unit>
</group>

‌

The problem is that the prefixes passed to the subfilters are the same, I think.

[Chase Tingley]

Fixed by https://bitbucket.org/okapiframework/okapi/pull-requests/538