#119 Trailing zero on small numbers

[Michael Kay]

When a numeric (double) value less than 0.001 is
converted to a string, the string contains a spurious
trailing 0.

For example,

<xsl:value-of select="0.00003"/>

outputs "0.000030"

The extra "0" is incorrect according to the XPath 1.0
rules for the string() function.

Present in 6.5.2, 7.3.1, and in all previous releases.

Test case: saxon36

Source code fixed in both branches.