Please use the new function otexstream.append(str, texrow) to append an
odocstringstream with texrow information to the output when outputing to a
string buffer (e.g. case of subcaptions).
otexstream used to count lines to build a TexRow, and some other things. The new
class otexrowstream has the line counting feature of the previous otexstream
without other stuff. otexstream is now a subclass of otexrowstream that has the
same features as before.
This is preliminary work for extending the cursor<->row tracking to math.
This resolves a dependency of src/support/docstream.cpp on src/TexRow.cpp,
which is the wrong way round. This fixes the linking
src/tests/check_ExternalTransforms with MSVC where the linker is not clever
enough to detect that the whole otexstream class is unused.
