49.4 Test cases for contrib_ode

The routines have been tested on a approximately one thousand test cases from Murphy, Kamke, Zwillinger and elsewhere. These are included in the tests subdirectory.

• The Clairaut routine ode1_clairaut finds all known solutions, including singular solutions, of the Clairaut equations in Murphy and Kamke.
• The other routines often return a single solution when multiple solutions exist.
• Some of the "solutions" from ode1_lie are overly complex and impossible to check.
• There are some crashes.