remove check for equality of double (singleValue != 0) in tubeSize

[mwetter]

tubeSize.c contains the code

... double singleVale ...
...
if (singleValue != 0) 

This needs to be changed as a double must not be compared for equality.

Also, the documentation is not clear as to what "singleValue" is and need to be improved, or the variable name be changed to something that better describes what it is.

[mwetter]

This is fixed on the master