Problem:    assert_fails() checks the last error message.
Solution:   Check the first error, it is more relevant.  Fix all the tests
            that rely on the old behavior.

Problem:    Not enough testing for restricted mode and function calls.
Solution:   Add more tests. (Yegappan Lakshmanan, closes #5847)

Problem:    Code in eval.c not sufficiently covered by tests.
Solution:   Add more tests. (Yegappan Lakshmanan, closes #5815)

Problem:    Warnings from MinGW compiler. (John Marriott) Json test fails when
            building without +float feature.
Solution:   Init variables. Fix Json parsing. Skip a few tests that require
            the +float feature.

Problem:    Various memory leaks reported by asan.
Solution:   Free the memory. (Ozaki Kiichi, closes #5003)

Problem:    More functions can be used as methods.
Solution:   Make various functions usable as a method.

Problem:    Negative float before method not parsed correctly.
Solution:   Apply "!" and "-" in front of expression before using ->.

Problem:    Confusing error when using a builtin function as method while it
            does not support that.
Solution:   Add a specific error message.

Problem:    Cannot use printf() as a method.
Solution:   Pass the base as the second argument to printf().

Problem:    Cannot use a lambda as a method.
Solution:   Implement ->{lambda}(). (closes #4768)