elisp-format: Accept null precision.

Proof that is is valid:
(format "%.f" 3.1415926)

* gettext-tools/src/format-elisp.c: Fix comment regarding the precision.
* gettext-tools/tests/format-elisp-1: Add a test case with null precision.

gettext-tools/src/format-elisp.c

@@ -31,8 +31,8 @@
 
 #define _(str) gettext (str)
 
-/* Emacs Lisp format strings are implemented in emacs-21.1/src/editfns.c,
-   xemacs-21.1.14/src/editfns.c and xemacs-21.1.14/src/doprnt.c.
+/* Emacs Lisp format strings are implemented in emacs-21.4/src/editfns.c and
+   emacs-21.4/src/doprnt.c.
    A directive
    - starts with '%' or '%m$' where m is a positive integer,
    - is optionally followed by any of the characters '#', '0', '-', ' ', '+',
@@ -40,7 +40,7 @@
    - is optionally followed by a width specification: '*' (reads an argument)
      or a nonempty digit sequence,
    - is optionally followed by '.' and a precision specification: '*' (reads
-     an argument) or a nonempty digit sequence,
+     an argument) or an optional nonempty digit sequence,
    - is finished by a specifier
        - '%', that needs no argument,
        - 'c', that need a character argument,

gettext-tools/tests/format-elisp-1

@@ -54,6 +54,8 @@ cat <<\EOF > f-el-1.data
 "abc%y"
 # Invalid: flags after width
 "abc%2^d"
+# Valid: null precision
+"abc%.f"
 # Invalid: twice precision
 "abc%.4.2d"
 # Valid: three arguments