doc: Update more docstrings to have one sentence summary as first line. Reviewed build-aux, libinterp/dldfcn, libinterp/octave-value, libinterp/parse-tree directories. * build-aux/mk-opts.pl, libinterp/dldfcn/__magick_read__.cc, libinterp/dldfcn/amd.cc, libinterp/dldfcn/audiodevinfo.cc, libinterp/dldfcn/audioread.cc, libinterp/dldfcn/ccolamd.cc, libinterp/dldfcn/chol.cc, libinterp/dldfcn/colamd.cc, libinterp/dldfcn/convhulln.cc, libinterp/dldfcn/dmperm.cc, libinterp/dldfcn/fftw.cc, libinterp/dldfcn/qr.cc, libinterp/dldfcn/symbfact.cc, libinterp/dldfcn/symrcm.cc, libinterp/octave-value/ov-base.cc, libinterp/octave-value/ov-bool-mat.cc, libinterp/octave-value/ov-cell.cc, libinterp/octave-value/ov-class.cc, libinterp/octave-value/ov-fcn-handle.cc, libinterp/octave-value/ov-fcn-inline.cc, libinterp/octave-value/ov-java.cc, libinterp/octave-value/ov-null-mat.cc, libinterp/octave-value/ov-oncleanup.cc, libinterp/octave-value/ov-range.cc, libinterp/octave-value/ov-struct.cc, libinterp/octave-value/ov-typeinfo.cc, libinterp/octave-value/ov-usr-fcn.cc, libinterp/octave-value/ov.cc, libinterp/parse-tree/lex.ll, libinterp/parse-tree/oct-parse.in.yy, libinterp/parse-tree/pt-binop.cc, libinterp/parse-tree/pt-eval.cc, libinterp/parse-tree/pt-mat.cc: doc: Update more docstrings to have one sentence summary as first line.

--- a/libinterp/octave-value/ov-null-mat.cc	Sun May 03 17:00:11 2015 -0700
+++ b/libinterp/octave-value/ov-null-mat.cc	Sun May 03 21:52:42 2015 -0700
@@ -97,9 +97,11 @@
        "-*- texinfo -*-\n\
 @deftypefn {Built-in Function} {} isnull (@var{x})\n\
 Return true if @var{x} is a special null matrix, string, or single quoted\n\
-string.  Indexed assignment with such a value on the right-hand side should\n\
-delete array elements.  This function should be used when overloading\n\
-indexed assignment for user-defined classes instead of @code{isempty}, to\n\
+string.\n\
+\n\
+Indexed assignment with such a value on the right-hand side should delete\n\
+array elements.  This function should be used when overloading indexed\n\
+assignment for user-defined classes instead of @code{isempty}, to\n\
 distinguish the cases:\n\
 \n\
 @table @asis\n\