Fixed various Undefined Behavior occurrences.

Conditionally uninitialized:
 - builtin_commandline.cpp:577
 - expand.cpp:869
 - parse_util.cpp:1036

Initialization of POD structs:
 - event.cpp:61
 - autoload.cpp:22

References used with va_start:
 - common.cpp:608:18

Found with clang-3.4's awesome -Wconditional-uninitialized,
-Wmissing-field-initializers and -Wvarargs.

common.h

@@ -689,7 +689,7 @@ wcstring wsetlocale(int category, const wchar_t *locale);
    \return zero if needle is not found, of if needle is null, non-zero otherwise
 */
 __sentinel bool contains_internal(const wchar_t *needle, ...);
-__sentinel bool contains_internal(const wcstring &needle, ...);
+__sentinel bool contains_internal(const wcstring needle, ...);
 
 /**
    Call read while blocking the SIGCHLD signal. Should only be called