Handle ln(rational multiple of e) better

Bug: 37486067

In particular, ln(e) is now a rational one.

Test: Unit tests, manual test.
Change-Id: I3cc57a4a84ec6667d3c8554c4fc234f9aa7c2e86
(cherry picked from commit bf2e69ae00d7b70562822769c100c3ddcc928b17)
1 file changed