doc: Update more docstrings to have one sentence summary as first line. Reviewed io, java, linear-algebra, prefs, and set script directories. * scripts/io/beep.m, scripts/io/dlmwrite.m, scripts/io/importdata.m, scripts/io/strread.m, scripts/io/textread.m, scripts/java/javaArray.m, scripts/java/java_get.m, scripts/java/java_set.m, scripts/java/javaaddpath.m, scripts/java/javachk.m, scripts/java/javaclasspath.m, scripts/java/javamem.m, scripts/java/javarmpath.m, scripts/linear-algebra/bandwidth.m, scripts/linear-algebra/commutation_matrix.m, scripts/linear-algebra/cond.m, scripts/linear-algebra/condest.m, scripts/linear-algebra/cross.m, scripts/linear-algebra/duplication_matrix.m, scripts/linear-algebra/expm.m, scripts/linear-algebra/housh.m, scripts/linear-algebra/isdefinite.m, scripts/linear-algebra/ishermitian.m, scripts/linear-algebra/issymmetric.m, scripts/linear-algebra/istril.m, scripts/linear-algebra/istriu.m, scripts/linear-algebra/krylov.m, scripts/linear-algebra/logm.m, scripts/linear-algebra/normest.m, scripts/linear-algebra/null.m, scripts/linear-algebra/onenormest.m, scripts/linear-algebra/orth.m, scripts/linear-algebra/qzhess.m, scripts/linear-algebra/rank.m, scripts/linear-algebra/rref.m, scripts/linear-algebra/vech.m, scripts/path/matlabroot.m, scripts/prefs/addpref.m, scripts/prefs/getpref.m, scripts/prefs/ispref.m, scripts/prefs/rmpref.m, scripts/prefs/setpref.m, scripts/set/powerset.m, scripts/set/setdiff.m: Update more docstrings to have one sentence summary as first line.

--- a/scripts/set/powerset.m	Sun May 03 12:58:42 2015 -0700
+++ b/scripts/set/powerset.m	Sun May 03 15:36:23 2015 -0700
@@ -24,9 +24,9 @@
 ## The set @var{a} must be a numerical matrix or a cell array of strings.  The
 ## output will always be a cell array of either vectors or strings.
 ##
-## With the optional second argument @qcode{"rows"}, each row of the set @var{a}
-## is considered one element of the set.  The input must be a 2-D numeric
-## matrix to use this argument.
+## With the optional argument @qcode{"rows"}, each row of the set @var{a} is
+## considered one element of the set.  The input must be a 2-D numeric matrix
+## to use this argument.
 ##
 ## @seealso{unique, union, intersect, setdiff, setxor, ismember}
 ## @end deftypefn