aliases/general: minor fixes

- Don't define some aliases if the target isn't installed, use _command_exists to check instead of `type` and `which`.
- Use `$EDITOR` for the editor for aliases about editing, excep the `sudo` ones because maybe you want those specifically?
- Fix `ls` aliases to match their common definitions (-A instead of -a: don't show '.' and '..' when displaying hidden files).

aliases/available/general.aliases.bash

@@ -9,8 +9,8 @@ fi
 # List directory contents
 alias sl=ls
 alias la='ls -AF' # Compact view, show hidden
-alias ll='ls -al'
-alias l='ls -a'
+alias ll='ls -Al'
+alias l='ls -A'
 alias l1='ls -1'
 alias lf='ls -F'
 
@@ -47,8 +47,8 @@ alias py='python'
 alias ipy='ipython'
 
 # Pianobar can be found here: http://github.com/PromyLOPh/pianobar/
-
-alias piano='pianobar'
+_command_exists pianobar \
+	&& alias piano='pianobar'
 
 alias ..='cd ..'         # Go up one directory
 alias cd..='cd ..'       # Common misspelling for going up one directory
@@ -69,11 +69,12 @@ alias md='mkdir -p'
 alias rd='rmdir'
 
 # Shorten extract
-alias xt='extract'
+_command_exists 'extract' \
+	&& alias xt='extract'
 
 # sudo editors
-alias svim='sudo ${VISUAL:-vim}'
-alias snano='sudo nano'
+alias svim='sudo "${VISUAL:-vim}"'
+alias snano='sudo "${ALTERNATE_EDITOR:-nano}"'
 
 # Display whatever file is regular file or folder
 function catt() {