Bug 784802 - Crop and rectangle-select tools incorrectly detect ...

... current aspect ratio

In gimp_{rectangle_select,crop}_tool_start(), move
GimpToolRectangle signal connection to the end of the function.  In
particular, connect the signals *after* the call to
gimp_{rectangle_select,crop}_tool_update_option_defaults(), since
it may result in an emission of a "change-complete" signal, whose
handler calls the function again with ignore_pending == FALSE, which
would override the ratio set with ignore_pending == TRUE.