[Bug-apl] Power Operator

[Christian Robert]

Got this stack trace while experimenting with the power operator. I'm not 
saying that what I was trying was correct/valid.

Xtian.

      {1+÷⍵}⍣= ⊢ 2
1.618033989
      {1+÷⍵}⍣0 ⊢ 2
2
      {1+÷⍵}⍣1 ⊢ 2
1.5
      {1+÷⍵}⍣2 ⊢ 2

==============================================================================
Assertion failed: _arg.how == 2
in Function:      eoc_LO
in file:          Bif_OPER2_POWER.cc:199

Call stack:

----------------------------------------
-- Stack trace at Bif_OPER2_POWER.cc:199
----------------------------------------
0x7fbb34bc0700 __libc_start_main
0x443a55  main
0x57abcd   Workspace::immediate_execution(bool)
0x48c43a    Command::process_line()
0x48c517     Command::do_APL_expression(UCS_string&)
0x4673b3      Bif_OPER2_POWER::eoc_LO(Token&)
0x455118       do_Assert(char const*, char const*, char const*, int)
========================================

SI stack:

Depth:    7
Exec:     0xd7b250
Safe ex:  no
Pmode:    ∇ λ1[1]
PC:       8 ENDL

==============================================================================
Assertion failed: tidx < line_txt.size()
in Function:      statement_text
in file:          Executable.cc:315

Call stack:
*** do_Assert() called recursively ***
==============================================================================
*** immediate_execution() caught other exception ***