bug#20421: 25.0.50; doc string of `insert-buffer-substring'

[Drew Adams]

Unlike the doc string of `insert', this doc string does not explicitly
say the following:

 Point and before-insertion markers move forward to end up
  after the inserted text.
 Any other markers at the point of insertion remain before the text.

It should.  Here is an example where a reader did not understand some
code, partly because, it seems, this doc string is not explicit about
this.

http://emacs.stackexchange.com/q/10904/105


In GNU Emacs 25.0.50.1 (i686-pc-mingw32)
 of 2014-10-20 on LEG570
Bzr revision: 118168 rgm@gnu.org-20141020195941-icp42t8ttcnud09g
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --enable-checking=yes,glyphs CPPFLAGS=-DGLYPH_DEBUG=1'