ftp/curl: Update to 7.51.0

• Update to 7.51.0
• Fixes 11 security vulnerabilities
• Remove docs no longer installed from plist

PR: 214000
MFH: 2016Q4
Security: 765feb7d-a0d1-11e6-a881-b499baebfeaf
Security: CVE-2016-8615
Security: CVE-2016-8616
Security: CVE-2016-8617
Security: CVE-2016-8618
Security: CVE-2016-8619
Security: CVE-2016-8620
Security: CVE-2016-8621
Security: CVE-2016-8622
Security: CVE-2016-8623
Security: CVE-2016-8624
Security: CVE-2016-8625