doc: Periodic grammarcheck of documentation. * doc/interpreter/contrib.txi, doc/interpreter/expr.txi, doc/interpreter/func.txi, doc/interpreter/linalg.txi, doc/interpreter/plot.txi, libinterp/corefcn/data.cc, libinterp/corefcn/debug.cc, libinterp/corefcn/graphics.cc, libinterp/corefcn/help.cc, libinterp/corefcn/load-save.cc, libinterp/corefcn/profiler.cc, libinterp/corefcn/syscalls.cc, libinterp/corefcn/utils.cc, libinterp/corefcn/variables.cc, libinterp/dldfcn/__init_fltk__.cc, scripts/general/deal.m, scripts/help/__gripe_missing_component__.m, scripts/miscellaneous/desktop.m, scripts/pkg/private/default_prefix.m, scripts/plot/appearance/__getlegenddata__.m, scripts/plot/util/pan.m, scripts/plot/util/rotate.m, scripts/plot/util/rotate3d.m, scripts/plot/util/zoom.m, scripts/signal/periodogram.m, scripts/specfun/factor.m, scripts/specfun/primes.m, scripts/statistics/base/lscov.m, scripts/testfun/private/compare_plot_demos.m, scripts/testfun/private/dump_demos.m, scripts/testfun/private/html_compare_plot_demos.m, scripts/testfun/test.m: Periodic grammarcheck of documentation.

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