Update documentation for 3.13 to notify customers of JRA-15648

Hi Andrew,

Can you please update the 3.13 Building JIRA from source doco to notify customers of JRA-15648 - a problem building JIRA 3.13 from source. Your call on whether to refer to JRA-15648 directly or include the fix in the doco.

Given that 3.13.1 will fix the problem, the doco should indicate that the problem is specific to 3.13 and is not in 3.13.x point releases (or any version after 3.13).

Thanks.

Cheers,
Ian