#18985: Improve fcntl documentation.

Original patch by Vajrasky Kok, further improved (I hope) by me.
diff --git a/Modules/fcntlmodule.c b/Modules/fcntlmodule.c
index de1e0da..6769098 100644
--- a/Modules/fcntlmodule.c
+++ b/Modules/fcntlmodule.c
@@ -27,7 +27,7 @@
 }
 
 
-/* fcntl(fd, opt, [arg]) */
+/* fcntl(fd, op, [arg]) */
 
 static PyObject *
 fcntl_fcntl(PyObject *self, PyObject *args)
@@ -77,11 +77,12 @@
 }
 
 PyDoc_STRVAR(fcntl_doc,
-"fcntl(fd, opt, [arg])\n\
+"fcntl(fd, op, [arg])\n\
 \n\
-Perform the requested operation on file descriptor fd.  The operation\n\
-is defined by op and is operating system dependent.  These constants are\n\
-available from the fcntl module.  The argument arg is optional, and\n\
+Perform the operation op on file descriptor fd.  The values used\n\
+for op are operating system dependent, and are available\n\
+as constants in the fcntl module, using the same names as used in\n\
+the relevant C header files.  The argument arg is optional, and\n\
 defaults to 0; it may be an int or a string.  If arg is given as a string,\n\
 the return value of fcntl is a string of that length, containing the\n\
 resulting value put in the arg buffer by the operating system.  The length\n\
@@ -90,7 +91,7 @@
 corresponding to the return value of the fcntl call in the C code.");
 
 
-/* ioctl(fd, opt, [arg]) */
+/* ioctl(fd, op, [arg]) */
 
 static PyObject *
 fcntl_ioctl(PyObject *self, PyObject *args)
@@ -104,7 +105,7 @@
        whereas the system expects it to be a 32bit bit field value
        regardless of it being passed as an int or unsigned long on
        various platforms.  See the termios.TIOCSWINSZ constant across
-       platforms for an example of thise.
+       platforms for an example of this.
 
        If any of the 64bit platforms ever decide to use more than 32bits
        in their unsigned long ioctl codes this will break and need
@@ -222,11 +223,12 @@
 }
 
 PyDoc_STRVAR(ioctl_doc,
-"ioctl(fd, opt[, arg[, mutate_flag]])\n\
+"ioctl(fd, op[, arg[, mutate_flag]])\n\
 \n\
-Perform the requested operation on file descriptor fd.  The operation is\n\
-defined by opt and is operating system dependent.  Typically these codes are\n\
-retrieved from the fcntl or termios library modules.\n\
+Perform the operation op on file descriptor fd.  The values used for op\n\
+are operating system dependent, and are available as constants in the\n\
+fcntl or termios library modules, using the same names as used in the\n\
+relevant C header files.\n\
 \n\
 The argument arg is optional, and defaults to 0; it may be an int or a\n\
 buffer containing character data (most likely a string or an array). \n\