[REVIEW] Support leading backslash as escape character in FXML

[Greg Brown]

This change would add support for a leading backslash as an escape character in FXML:

http://javafx-jira.kenai.com/browse/RT-18680

UEL uses a leading backslash as an escape character for expression values. For consistency, FXML should probably also support this convention. For backwards compatibility, we would also preserve the existing convention of doubling up the resolution operator as an escape sequence. So, for example, both of the following would be supported and would produce a Label instance with text "$foo":

<Label text="$${foo}"/>
<Label text="\${foo}"/>

Comments/questions welcome.

Thanks,
Greg