Various bugs in string comparison functions

[bennylp]

Bug in pj_strcmp2() will cause pj_strcmp2("1", "12") to return equal.

Checking other string functions reveals that some string comparison functions are not exactly compliant with ANSI. For example, given:

  char *s1 = "2";
  char *s2 = "11";

With ANSI, strcmp(s1, s2) will return 1, while with pj_strcmp(s1, s2) will return -1.