my/m4/my_check_docbook_ns_xslt_min.m4: new

replace the AX_CHECK_DOCBOOK_XSLT_MIN macro with a MY_CHECK_DOCBOOK_NS_XSLT_MIN
macro that checks for the *namespaced* variant of the DocBook
stylesheets.
Merge branch 'master' of ../libmy
build system: switch from AX_CHECK_DOCBOOK_XSLT_MIN to MY_CHECK_DOCBOOK_NS_XSLT_MIN

AX_CHECK_DOCBOOK_XSLT_MIN checks that the non-namespaced docbook
stylesheets are available, while the makefile was building using the
namespaced stylesheets. replace the autoconf check with one that
corresponds to the actual (namespaced) stylesheets that are used in the
build.

(fixes #1)
.travis.yml: don't install docbook-xsl

docbook-xsl is no longer necessary now that issue #1 is fixed.
Revert "README.md: add docbook-xsl to the recommended debian packages for building the documentation"

This reverts commit 78c2eeedd029d66fa506bb2ad2483e7b70bd9f96.
input_seqsrc: update the counters on input->stream immediately

previously the seqsrc tracking code would only update
input->stream->count_drop and input->stream->count_recv when individual
seqsrc objects were garbage collected in _input_seqsrc_get(), or when
seqsrc tracking for an entire stream was shut down in
_input_seqsrc_destroy().

we want to be able to export the drop and recv counters for an entire
input stream on demand and for these counters to be accurate, so
increase the input stream counters immediately.
input: don't modify input->stream counters from seqsrc internals

ideally the input->stream->count_recv counter should be retrievable
without seqsrc tracking enabled, so increment count_recv in
_input_nmsg_read_container_sock() instead.

also, it's not necessary for the seqsrc tracking code to be responsible
for updating input->stream->count_drop. instead, return the number of
dropped containers from _input_seqsrc_update() and do the update of
input->stream->count_recv from _input_nmsg_read_container_sock().  this
keeps all the input->stream counter updates in the same function.
input: new interfaces for retrieving container counters

this adds two new exported functions,
nmsg_input_get_count_container_received() and
nmsg_input_get_count_container_dropped(), which retrieve the internal
count_recv and count_drop counters for input stream sockets.

(fixes #2)
configure.ac: bump version to 0.8.0-rc2
ChangeLog: 0.8.0-rc2
Merge tag 'tags/v0.8.0_rc2' into debian
debian/libnmsg6.symbols: 0.8.0~rc2 update
debian/changelog: 0.8.0~rc2-1