Report error when an invalid but ok looking formula is entered

[Former user]

Originally reported on Google Code with ID 331

Sometimes a user can enter an invalid formula in the calculator. The
formula can look for user as an valid one. The SpeedCrunch does not report
error but calculates the formula ignoring unknown entities.  

What steps will reproduce the problem?
1. Try to reproduce Issue 330 where the problem was "character in the  
page is not the same as the '-' in your keyboard"
OR
1. enter formula like '5 + 8 : 4'
OR
something similar

What is the expected output? What do you see instead?
An error message that the formula is invalid. Instead you get a false
result eg. for '234 : 4' you get '234'. Which is dangerous since in some
other applications (or regions) or written text, the ':' is a valid
division letter.

What version of the product are you using? On what operating system?
Kubuntu 9.10 ,  SpeedCrunch version : 0.10.1

Please provide any additional information below.

thanks

Reported by balique on 2010-03-11 18:19:20

[Former user]

``` Thanks. I consider this more of a defect than a request, actually. ```

Reported by `helder.pereira.correia` on 2010-03-11 19:05:57 - Status changed: `Accepted` - Labels added: Type-Defect, Priority-Critical, OpSys-All, Milestone-0.11, Component-Logic, Usability

[Former user]

``` Issue 342 has been merged into this issue. ```

Reported by `helder.pereira.correia` on 2010-04-19 17:47:25

[Former user]

``` Fixed in commit ea2aff5c8185b7792c8c0e9555cf0dd11e44f9aa. ```

Reported by `helder.pereira.correia` on 2010-10-31 08:37:14 - Status changed: `Fixed`