When load-force-doc-strings is true, read (#$ . POS) as the (unibyte)
string referred to.  This feature was lost by mistake in the recent
nonrecursive reader rewrite.

Noticed by Stefan Monnier.

* src/lread.c (get_lazy_string): New function (code mostly recycled
from an old version).
(read0): Detect (#$ . FIXNUM) and retrieve the string if appropriate.
* test/src/lread-resources/lazydoc.el:
* test/src/lread-tests.el (lread-force-load-doc-strings):
New test.

* test/data/emacs-module/mod-test.c: Move from here...
* test/src/emacs-module-resources/mod-test.c: ...to here.
* test/src/emacs-module-tests.el (ert-x): Require.
(mod-test-file, module/describe-function-1):
* test/Makefile.in (test_module_dir): Adjust for move.

* test/data/files-bug18141.el.gz: Move from here...
* test/lisp/files-resources/files-bug18141.el.gz: ... to here.
* test/lisp/files-tests.el (ert-x): Require.
(files-test-bug-18141-file): Use ert-resource-file.

* test/data/mailcap/mime.types: Move from here...
* test/lisp/net/mailcap-resources/mime.types: ...to here.
* test/lisp/net/mailcap-tests.el (ert-x): Require.
(mailcap-tests-path): Use ert-resource-file.

* test/data/somelib.el:
* test/data/somelib2.el: Move from here...
* test/src/lread-resources/somelib.el:
* test/src/lread-resources/somelib2.el: ...to here.
* test/src/lread-tests.el (ert, ert-x): Require.
(lread-test-bug26837): Use ert-resource-directory.

* test/data/syntax-comments.txt: Move from here....
* test/src/syntax-resources/syntax-comments.txt: ...to here.
* test/src/syntax-tests.el (ert-x): Require.
(syntax-comments, syntax-br-comments, syntax-pps-comments):
Use ert-resource-file.

* test/data/xref/file1.txt:
* test/data/xref/file2.txt: Move from here...
* test/lisp/progmodes/xref-resources/file1.txt:
* test/lisp/progmodes/xref-resources/file2.txt: ...to here.
* test/lisp/progmodes/xref-tests.el (ert, ert-x): Require.
(xref-tests-data-dir): Use ert-resource-directory.