ssl: Certificates and PEM-cache cleaning fixed to avoid memory leak

Certificate db cleaning messages where sent to the wrong process after
restructuring to avoid bottlenecks.

It is possible that the ssl manager process gets two cleaning messages
for the same entry. E.i. first cleaning message is sent and before it
is processed a new reference is allocated  and again released for the
entry, generating a second cleaning message.

Also in ssl_manger:handle_info/2 it is possible that there exists a
new reference to an "old" file name with a potential new content.
Fixed specs
[erl_docgen] Fix pdf indentation bug for tagged lists
[erl_docgen] Fix dtd error for type_desc tag
[erl_docgen] Add xmllint target for the documentation and fix some DTD errors
[erl_docgen] Update vsn.mk
[erl_docgen] Fix include path to xmllint
Merge branch 'fredrik/public_key/specs-r16/OTP-10723'

* fredrik/public_key/specs-r16/OTP-10723:
  Fixed specs
Merge branch 'lars/erl_docgen/indenterings-bug/OTP-10725'

* lars/erl_docgen/indenterings-bug/OTP-10725:
  [erl_docgen] Fix include path to xmllint
  [erl_docgen] Update vsn.mk
  [erl_docgen] Add xmllint target for the documentation and fix some DTD errors
  [erl_docgen] Fix dtd error for type_desc tag
  [erl_docgen] Fix pdf indentation bug for tagged lists
Merge branch 'master' of super:otp

* 'master' of super:otp:
  Fixed specs
Merge branch 'ia/ssl/certtable-clean/OTP-10710'

* ia/ssl/certtable-clean/OTP-10710:
  ssl: Certificates and PEM-cache cleaning fixed to avoid memory leak