proftpd: upgrade to 1.3.5a

1. 1.3.5a includes the fix for CVE-2015-3306:
https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2015-3306


2. replace the proftpd generated libtool with the native libtool
which support the sysroot

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>