Cannot render half arrow

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Put an arrow on a canvas
2. Change arrow type to half arrow by writing lt=-\> (according to this site: 
http://www.itmeyer.at/umlet/faq/How%20to%20create%20connections%20in%20sequence%
20diagrams.htm)

What is the expected output? What do you see instead?
Expected: Half arrow is drawn
Instead: Invalid value error

What version of the product are you using? On what operating system?
13.0 August 2014

Please provide any additional information below.
I know it's possible to make half-arrow in Sequence All-in-one diagram, but it 
doesn't work when you draw diagram on your own.

Original issue reported on code.google.com by lesniews...@gmail.com on 29 Sep 2014 at 2:10

[GoogleCodeExporter]

The half-arrowhead is outdated and isn't used anymore since UML 1.4
see http://www.informit.com/articles/article.aspx?p=169507&seqNum=3 and 
especially 
http://ptgmedia.pearsoncmg.com/images/chap4_0321193687/elementLinks/04fig05.gif

Perhaps we will still add it in future, but this can be the reason why it's 
currently missing.

Original comment by AFDiaX on 5 Oct 2014 at 7:17