Bug 137751

Description:
there was an old bug recently solved: tdf#44076, 

imho the fix is incomplete as it doesn't work for e.g. '=-8^(2/3)', 

'=-8^(2/3)' and '=-27^(2/3)' are! 'calculateable terms', even in calc, if you rearrange them to '=-8^2^(1/3)' or '=-8^(1/3)^2', 

as @Christopher likes to keep that report closed and requested a new bug ... here we go, 

@xisco, pls. do not! close duplicate, acc. @Christoper it's a different issue ... and it's not resolved! 

ok? 

follow up to: tdf#44076, 
related: tdf#69293, tdf#121398, 

P.S. an expanded task would be to solve the handling of (-8)^(2/6), calculate straightforward and get 2, or reduce the fraction to '1/3' first and get -2? there might be a math rule for that, but i missed it in school and couldn't find it on the web ... a help might be that 4^1/2 is not! 2, but [-2/2], 

Steps to Reproduce:
1. enter '=(-8)^(2/3)' in a cell, without the quotes, 
2. hit enter
3. observe #NUM! as result

Actual Results:
#NUM!

Expected Results:
4


Reproducible: Always


User Profile Reset: No



Additional Info:
tested with: 
Version: 7.1.0.0.alpha0+ (x64)
Build ID: 586f6abee92af3cdabdce034b607b9a046ed3946
CPU threads: 8; OS: Windows 6.1 Service Pack 1 Build 7601; UI render: default; VCL: win
Locale: de-DE (de_DE); UI: en-US
Calc: