Make consistent the usage of variable names in the function definitions found in...

Make consistent the usage of variable names in the function definitions found in the Texinfo docs.

* doc/r5rs/r5rs.texi:
* doc/ref/api-compound.texi:
* doc/ref/api-data.texi:
* doc/ref/api-debug.texi:
* doc/ref/api-evaluation.texi:
* doc/ref/api-io.texi:
* doc/ref/api-modules.texi:
* doc/ref/api-procedures.texi:
* doc/ref/api-scheduling.texi:
* doc/ref/api-smobs.texi:
* doc/ref/compiler.texi:
* doc/ref/misc-modules.texi:
* doc/ref/posix.texi:
* doc/ref/scheme-using.texi:
* doc/ref/srfi-modules.texi:
* doc/ref/vm.texi:
* doc/ref/web.texi:
* doc/sources/env.texi: Make usage of variable names of function definitions
  more consistent.