gnucash unstable: Fix use of guile function introduced in 2.0.10, not available in Ubuntu14.04.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/19412de2 (commit)
	from  https://github.com/Gnucash/gnucash/commit/6e9025d2 (commit)



commit 19412de2216a624a6a27e4f1afd4264deb8e57aa
Author: John Ralls <jralls at ceridwen.us>
Date:   Fri Dec 22 11:07:29 2017 -0800

    Fix use of guile function introduced in 2.0.10, not available in Ubuntu14.04.
    
    Also generalize KVP type detection so that signed and unsigned values\nare appropriately converted.



Summary of changes:
 libgnucash/engine/kvp-scm.cpp | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)