Merge InstructionError and ProgramError

From the user's perspective, it's just an instruction error.
For program-specific errors, we still have
InstructionError::CustomError.

programs/token/src/lib.rs

@@ -1,9 +1,9 @@
 use bincode::serialize;
 use log::*;
 use solana_sdk::account::KeyedAccount;
-use solana_sdk::native_program::ProgramError;
 use solana_sdk::pubkey::Pubkey;
 use solana_sdk::solana_entrypoint;
+use solana_sdk::transaction::InstructionError;
 
 mod token_program;
 
@@ -13,11 +13,11 @@ fn entrypoint(
     info: &mut [KeyedAccount],
     input: &[u8],
     _tick_height: u64,
-) -> Result<(), ProgramError> {
+) -> Result<(), InstructionError> {
     solana_logger::setup();
 
     token_program::TokenProgram::process(program_id, info, input).map_err(|e| {
         error!("error: {:?}", e);
-        ProgramError::CustomError(serialize(&e).unwrap())
+        InstructionError::CustomError(serialize(&e).unwrap())
     })
 }