Change name of dev version

Needed to conform with pep440, change 1.5.x to 1.5.dev1

Without this change I get warnings about the version not conforming with pep 440 https://www.python.org/dev/peps/pep-0440/

With the newly released version of pip (6.0) 1.5.x is being regarded as smaller that all releases (1.4.2 etc.) 
1.5.devN are allowed names and correctly handled as > 1.4.N and < 1.5.0, 1.5.0rcN etc.