MingW32/Cygwin build fix

[Ident]

Original report by Anonymous.

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Automatic migration. Original reporter: "Dalfy"

CEGUI does not build correctly on Mingw32 / Cygwin

MINGW and CYGWIN compatability
This patch converts all render, xmlparser, and major
header files to allow both MINGW and CYGWIN to compile
cegui. neither platform accept __declspec(dllimport).

Imported from sourceforge on July 16, 2006
Submitted by macguyvok

Reproducibility: always

Additional information: This patch makes it possible to compile on MinGW,
though more work is needed to get it to work on MSYS.
Essentially MinGW throws warnings when is sees
__declspec(dllimport), so these are defined out if
MINGW32 is seen, which is defined by the compiler.
Also MinGW's std::exception doesn't accept a parameter
in it's constructor, so these and their corresponding
catches were replaced with CEGUI::String for MinGW only.

OS: Windows, OS build: all, Platform: MingW32

[Ident]

Original comment by Anonymous.

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Original reporter: Dalfy

I am closing this ticket cause its the same as ticket 55