Replace pow(10, foo) with array dereference

Aside from being much faster, Windows was occasionally returning
e.g. 99 instead of 100 for pow(10, 2).  This stops that and thus
fixes:
Bug 721447 - Entries with values of ,50 are imported as ,51
Bug 721825 - Online prices displayed as unreadable fractions in 2.6.0

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23720 57a11ea4-9604-0410-9ed3-97b8803252fd
Fix configure's use of gnc-scm-info for out-of-tree builds.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23721 57a11ea4-9604-0410-9ed3-97b8803252fd