Based on patches by Henri Verbeet.

Fix a byte vs. WCHAR count issue in test_hkey_main_Value_W().
Check that RegQueryValueEx[AW]() did not write more data than expected.

REG_EXPAND_SZ must be exported as hexadecimal to preserve the string type.
0-byte strings and those missing a trailing '\0' or with odd sizes must 
be saved as hexadecimal too so they are restored as is.
Move the binary-value export code to the new REGPROC_export_binary() 
function.

We already know it in the caller so this saves us one lstrlenW() call.

This fixes a major buffer overflow bug in 'regedit /E'.