GroupDetectors should be cleverer with file type

[martyngigg]

This issue was originally TRAC 5033

If you give GroupDetectors an XML file with a '.map' extension it falls over immediately.

I would think it be possible to peek at the first line and if it has an <?XML tag then assume it's XML

[martyngigg]

@NickDraper (2012-04-30T14:15:52):
Moved at end of release 2.1

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@NickDraper (2012-08-10T12:45:14):
http://www.mantidproject.org/Release_Notes_2_2_Full_List

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@NickDraper (2012-10-28T11:42:53):
Moved to release 2.4

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@NickDraper (2013-01-28T09:23:34):
Moved at the code freeze for release 2.4

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@NickDraper (2013-04-29T09:50:07):
Moved to r2.6 at the end of r2.5

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@NickDraper (2013-07-26T13:59:10):
Moved to the Backlog after the code freeze for R2.6

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@NickDraper (2014-02-14T11:07:57):
bulk move to assigned at the into of the triage step

[shahrozahmed1]

This issue seems to have been fixed

[FedeMPouzols]

This is working. GroupDetectors v2 supports xml and map extensions, and also the algorithm dialog gives a explicit list of extensions/formats: xml/map/all files.