faketime wrapper complains when env vars are set unless comp/w SILENT (closes #307)

src/Makefile

@@ -80,6 +80,10 @@
 #           ld automatically choose the correct library version to use for the
 #           target binary. Use for Linux platforms with Multi-Arch support only!
 #
+#     SILENT
+#         - avoid that the faketime wrapper complains when running within a
+#           libfaketime environment
+#
 #   * Compilation addition: second libMT target added for building the pthread-
 #     enabled library as a separate library
 #

src/faketime.c

@@ -114,6 +114,12 @@ int main (int argc, char **argv)
   bool fake_pid = false;
   const char *pid_val;
 
+#ifndef SILENT
+  if (getenv("FAKETIME") || getenv("FAKETIME_SHARED") || getenv("FAKETIME_FAKEPID") || getenv("FAKERANDOM_SEED")) {
+    fprintf(stderr, "faketime: You appear to be running faketime within a libfaketime environment. Proceeding, but check for unexpected results...\n");
+  }
+#endif
+
   while (curr_opt < argc)
   {
     if (0 == strcmp(argv[curr_opt], "-m"))