bug#15136: get-string-all documentation

[Josep Portella Florit]

Hi!

In the documentation for get-string-all, on module (rnrs io ports), it
says:

    Scheme Procedure: get-string-all textual-input-port count

But it really only receives one argument, not two.

Link to the error in the documentation source: 
http://git.savannah.gnu.org/cgit/guile.git/tree/doc/ref/api-io.texi#n1935

Link to get-string-all definition for comparison:
http://git.savannah.gnu.org/cgit/guile.git/tree/module/rnrs/io/ports.scm#n459

Josep